EP2640429B1

EP2640429B1 - Bone void fillers

Info

Publication number: EP2640429B1
Application number: EP11791697.3A
Authority: EP
Inventors: Rama Akella; Ian Ross Garrett; Hai Bo Wen; Shuliang Li; Dean M. Acker; Nichole Wilhelm
Original assignee: Zimmer Orthobiologics Inc
Current assignee: Zimmer Orthobiologics Inc
Priority date: 2010-11-15
Filing date: 2011-11-15
Publication date: 2016-12-21
Anticipated expiration: 2031-11-15
Also published as: US8613938B2; CA2817584A1; AU2011329054A1; CA2817584C; CN103313733A; JP2013542837A; EP2640429A1; WO2012068135A1; US20120121660A1; AU2011329054B2

Description

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of U.S. application Serial No. 61/413,502, filed on November 15, 2010 and U.S. application Serial No. 61/541,690, filed on September 30, 2011 , under 35 U.S.C. § 119(e).

FIELD OF THE INVENTION

The field of the invention relates generally to bone void filler compositions, the preparation of the bone void filler compositions, and use of the bone void filler compositions, e.g., in promoting bone growth.

BACKGROUND

In the fields of orthopedics (e.g., reconstructive, trauma, spine, and dentistry), effective repair of bone defects, which may have been caused by disease, injury, wounds, or surgery, has long been a goal. A number of materials and compositions have been considered, evaluated, or used. Beyond their ability to promote bone growth, the biological, physical, and mechanical properties of the materials and compositions are factors, among others, affecting their suitability and performance in various applications.
Bone grafting has been commonly used to augment healing in treating a variety of musculoskeletal disorders. Grafting techniques in this field have been practiced for over 100 years and include procedures employing autograft, allograft and xenograft materials. Autologous cancellous bone is considered the standard against which other treatments are evaluated. Autograft cancellous bone is non-immunogenic and has all the appropriate structural and functional characteristics appropriate for the particular recipient. Autograft cancellous bone provides both a natural tissue scaffold and osteoinductive growth factors and may also contain osteogenic components (e.g., mesenchymal stem cells) if obtained with bone marrow. Autologous cancellous bone, however, is not acceptable or otherwise available for all patients. Autograft sources, as well as allograft sources, are relatively limited and may be expensive or painful to obtain. These and other limitations of autografts and allografts have resulted in alternative compositions being pursued as graft substitutes to fill defects (e.g., voids) in bone. Numerous bone graft substitutes having osteoinductive and/or osteoconductive properties have been explored and include, but are not limited to, products containing hydroxyapatites, tricalcium phosphates, aliphatic polyesters (poly(lactic) acids (PLA), poly(glycolic)acids (PGA), and polycaprolactone (PCL)), polyhydroxybutyrate (PHB), cancellous bone allografts, human fibrin, plaster of Paris, apatite, wollastonite (calcium silicate), bioactive glasses, ceramics, titanium, devitalized bone matrix, non-collagenous proteins, collagen, and autolyzed antigen extracted allogenic bone.
Demineralized bone, in the form of scaffold, granules, particulate, and/or powder, has been used in certain bone graft substitutes due to its osteoinductive properties. Osteoinductive components induce bone formation by stimulating stem cells and osteoprogenitor cells to undergo the osteogenic differentiation pathway. In the 1960's, demineralized bone was observed to induce the formation of new cartilage and bone when implanted in ectopic sites (Urist, 1965, Science 150:893-899). Demineralized bone can be prepared by grinding a bone, demineralizing it with an acid solution, washing with water or a phosphate buffered solution, washing with ethanol and drying it. Demineralized bone may be obtained from a source such as a commercial bone or tissue bank (e.g., AlloSource, Denver Colo.). WO 2008/019024 A2 and WO 2004/091435 A2 describe bone graft compositions.

SUMMARY

The present invention provides bone void filler compositions, methods to prepare bone void filler compositions, and uses of bone void filler compositions, for example, to promote bone growth. For instance, in one example, the present invention includes bone void filler compositions containing an acidic mineral component, an osteoinductive component that contains demineralized bone (DMB) which comprises collagen, and a biologically acceptable osteoconductive carrier component as claimed in claim 1.
In accordance with one aspect of the invention, there is provided a bone void filler composition containing an acidic mineral component that contains a calcium source and a phosphate source or a lower alkyl carboxylate source, e.g., R-COO^- where R is (CH₃)(CH₂)_n where n is 0, 1, 2, 3 or 4, such as a mineral salt; an osteoinductive component that contains demineralized bone which comprises collagen; and a three-dimensional, osteoconductive biologically acceptable carrier component that contains a collagenous material. In one embodiment, there is provided a bone void filler composition containing an acidic mineral component that contains a calcium source and a phosphate source, an osteoinductive component that contains demineralized bone and a three-dimensional, osteoconductive biologically acceptable carrier component that contains a collagenous material. The acidic mineral component in the composition is present in the range of about 1% to about 60% by weight relative to the combined weight of the acidic mineral component and the total weight of the collagen, accounting for collagen contained in the carrier as well as any collagen found in other components, including the demineralized bone. In one embodiment, the acidic mineral component comprises CaHPO₄2H₂O or calcium acetate. In one embodiment, the acidic mineral component is a self-setting cement, such as brushite (calcium hydrogen phosphate dihydrate (CaHPO₄•2H₂O)) cement, which when included with other components disclosed herein, provides for a self-setting bone void filler composition.
The bone void filler composition may be in the form of a sponge or in the form of a paste or putty, e.g., a paste or putty obtained from particulated sponge or from rehydrated sponge. The sponge, paste or putty may include additional components, e.g., one or more components that improve retention of demineralized bone particles, improve extrudability, e.g., from a syringe or through a cannulated device, improve cohesiveness in water or other physiologically compatible liquid carriers, improve moldability, improve shape retention during irrigation, and/or improve structural integrity, or any combination thereof, relative to a sponge, paste or putty without the additional component(s). A putty or paste of the invention may be injected or introduced to a mold, or manipulated without use of a device. In certain embodiments, a paste or putty may have a more dynamic three-dimensional structure than a sponge. For example, a putty or paste has a three-dimensional shape which can be altered but which has a volume which is substantially the same after being subjected to a force that results in the altered shape. A sponge has a three-dimensional shape and volume which can be altered, e.g., by compression, but is capable of having the same shape and volume after the force that alters the shape and volume is removed.
In one embodiment, the bone void filler composition comprises an acidic calcium phosphate component from about 8 wt% to about 12 wt% of the composition; an osteoinductive demineralized bone component from about 70 wt% to about 80 wt% of the composition; and an osteoconductive collagen carrier component from about 10 wt% to about 16 wt% of the composition; wherein the composition is in the form of a porous three dimensional structure. In one embodiment, the bone void filler composition of claim 1, wherein the acidic calcium phosphate component comprises monocalcium phosphate monohydrate [Ca(H₂PO₄)2H₂O]; calcium hydrogen phosphate dihydrate [CaHPO₄2H₂O], amorphous calcium phosphate [Ca₃(PO₄)2H₂O], anhydrous calcium hydrogen phosphate [CaHPO₄], partially dehydrated calcium hydrogen phosphate [CaHPO₄xH₂O, where x is between 0 and 2], and/or calcium pyrophosphate (Ca₂O₇P₂)[2CaO₂P₂O₅]. In one embodiment, the composition has a pH from about 2 to about 7, for example, a pH from about 3 to about 5. In one embodiment, the demineralized bone is in a form selected from a powder, particle, granule, fiber, and combinations thereof. For example, the demineralized bone particle or granule size may be from about 105 µm to about 850 µm. In one embodiment, the demineralized bone component comprises human demineralized bone. In one embodiment, the osteoconductive collagen carrier component comprises non-human mammalian collagen, e.g., bovine collagen. In one embodiment, the osteoconductive collagen carrier component comprises Type I and/or Type III collagen, for instance, more than about 90 wt% Type I and less than about 10 wt% Type III collagen. In one embodiment, the porous three dimensional structure is in the form of a strip, disc, sheet, bullet or cylinder, or is shaped for dental ridge augmentation. In one embodiment, the bone void filler composition further comprises an additive selected from the group consisting of allograft chips, bioceramics, biocomposites, calcium salts other than the acidic calcium phosphate component, phosphate salts other than the acidic calcium phosphate component; and combinations thereof. In one embodiment, the bone void filler composition further comprises an additive selected from the group consisting of bioresorbable fibers, synthetic polymers, and combinations thereof. In one embodiment, the bone void filler composition further comprises a liquid carrier selected from selected from the group consisting of biological fluids selected from the group consisting of bone marrow aspirate, whole blood, serum, and/or plasma; biocompatible liquids selected from the group consisting of water, saline and/or aqueous buffers; and combinations thereof. In one embodiment, the liquid carrier comprises bone marrow aspirate and saline.
In one embodiment, the bone void filler composition further comprises a collageneous biologically acceptable carrier component or a biocompatible, bioresorbable fiber, such as a glass fiber, a synthetic polymer, for instance, a synthetic biodegradable polymer, or other material that enhances load bearing properties, including but not limited to woven, non-woven (e.g., electrospun), mesh or struts. The collagenous biologically acceptable carrier component may differ in source (e.g., human versus bovine collagen, or collagen from bone versus collagen from skin) or type (e.g., fibrillar collagen or denatured collagen) from the collagen or collagenous material in the osteoinductive component or the osteoconductive component. In one embodiment, the collageneous biologically acceptable carrier comprises a gelatin or heat denatured and solubilized collagen. A synthetic biodegradable polymer includes but is not limited to polyvinylpyrrolidone, aliphatic polyesters (poly(lactic) acids (PLA), poly(glycolic)acids (PGA), poly(dl-lactide-co-glycolide) (PLGA), polycaprolactone (PCL)), or polyhydroxybutyrate (PHB) in either homopolymer or copolymer form. The bioresorbable fiber may be in the form of a mesh to encapsulate the other components, which mesh improves the structural integrity of the composition. In one embodiment, the inclusion of a biocompatible, bioresorbable fiber in the bone void filler composition may allow for the use of lower amounts of the collagenous biologically acceptable carrier component, e.g., where the fiber also provides a scaffold.
Also described is a self-setting bone void filler composition comprising an acidic mineral component that contains a calcium source and a phosphate or sulfate source, an osteoinductive component that contains demineralized bone, a three-dimensional, osteoconductive biologically acceptable carrier component that contains a collagenous material, and a self-setting calcium containing cement. In one embodiment, a self-setting calcium containing cement includes a calcium phosphate cement such as brushite cement, hydroxyapatite cement, or calcium sulfate cement. The self-setting brushite cement can be produced by mixing beta-tricalcium phosphate (beta-TCP) with orthophosphoric acid or by mixing beta-TCP with pyrophosphoric acid or b mixing beta-TCP and monocalcium phosphate (MCP) with water or by mixing beta-TCP and MCP with glycolic acid or with citric acid. Self-setting hydroxyapatite cement can be produced by mixing tetracalcium phosphate (TTCP) and dicalcium phosphate dihydrate (DCPD) with water or sodium hydrogen phosphate (Na₂HPO₄) or by mixing alpha-TCP, calcium carbonate and monocalcium phosphate monohydrate (MCPM) with water, or by mixing alpha-TCP and MCMP, or by mixing MCPM with HA or by mixing beta-TCP with MCMP with water. The calcium sulfate cement can be produced by mixing calcium sulfate powder with water. The self-setting calcium containing cement in the composition is present in the range of about 10% to about 60% by weight relative to the combined weight of the acidic mineral component and the total weight of the collagen, accounting for collagen contained in the carrier as well as any collagen found in other components, including the demineralized bone. For example, the self-setting calcium phosphate cement in the composition is present in the range of about 10% to about 60% by weight relative to the combined weight of the acidic mineral component and the total weight of the collagen, accounting for collagen contained in the carrier as well as any collagen found in other components, including the demineralized bone.
Also described is a self-setting bone void filler composition comprising an acidic mineral component that contains a calcium source and a phosphate source, an osteoinductive component that contains demineralized bone, a three-dimensional, osteoconductive biologically acceptable carrier component that contains a collagenous material, and a self-setting polymer. In one embodiment, the self-setting polymer is a thermal sensitive biodegradable block copolymer which is dissolved in aqueous solution at or below the room temperature and transits into a gel phase at body temperature as the bone void filler composition is applied to the grafting site. Thermal sensitive biodegradable block copolymers include but are not limited to PEG/PLA and PEG/PLGA diblock and triblock copolymers, PEG/PCL diblock and tribock copyolymer, polyethylene glycol grafted chitosan, or poly(dimethyl-β-malic acid-co-β-butyrolactone)/poly(lactic acid). In one embodiment, a self-setting biodegradable polymer system is 4-arm polyethylene glycol succinimidyl glutarate and albumin or 4-arm polyethylene glycol succinimidyl glutarate and 4-arm polyethylene glycol amine. The self-setting biodegradable polymer in the composition is present in the range of about 10% to about 50% by weight relative to the combined weight of the acidic mineral component and the total weight of the collagen, accounting for collagen contained in the carrier as well as any collagen found in other components, including the demineralized bone. In one embodiment, the self-setting polymer is a non-resorbable polymer which includes but is not limited to poly(methyl methacrylate) PMMA cement, poloxamer. In one embodiment, a bone void filler composition having a self-setting component that results in a self-setting formulation is useful in certain clinical situations, e.g. sinus lift, ridge augmentation, tooth extraction socket, etc.
Also described is a pre-mixed bone void filler composition containing an acidic mineral component that contains a calcium source and a phosphate source or a lower alkyl carboxylate source; an osteoinductive component that contains demineralized bone; and a biologically acceptable carrier component that includes a liquid carrier. In one embodiment, there is provided a premixed bone void filler composition containing an acidic mineral component that contains a calcium source and a phosphate source, an osteoinductive component that contains demineralized bone, and a biologically acceptable carrier component that includes a liquid carrier. In one embodiment, the acidic mineral component comprises CaHPO₄ or its hydrate form (e.g., CaHPO₄2H₂O) or calcium acetate. The ratio of demineralized bone component to acidic mineral component ranges from about 0.5:1 to about 80:1. The pre-mixed bone void filler composition may be in the form of a paste or putty, which is malleable, extrudable, and retains its shape during irrigation or handling in water or other physiologically compatible liquid carriers. The paste or putty may include additional components, e.g., those that improve retention of demineralized bone particles, improve extrudability, e.g., from a syringe, improve cohesiveness in water or other physiological compatible liquid carriers, improve moldability and/or improve shape retention during irrigation, or any combination thereof, relative to a paste or putty without the additional component(s). A paste or putty of the invention may be injected or introduced to a mold, or manipulated without use of a device. In certain embodiments, a paste or putty may have a more dynamic three-dimensional structure than a sponge.
Also described is a premixed bone void filler composition containing an acidic mineral component that contains a calcium source and a phosphate source or a lower alkyl carboxylate source; an osteoinductive component that contains demineralized bone; and a biologically acceptable carrier component that includes a liquid carrier. In one embodiment, there is provided a premixed bone void filler composition containing an acidic mineral component that contains a calcium source and a phosphate source an osteoinductive component that contains demineralized bone; and a biologically acceptable carrier component that includes a liquid carrier. In one embodiment, the acidic mineral component comprises CaHPO₄ or its hydrate form (e.g., CaHPO₄2H₂O) or calcium acetate. The ratio of demineralized bone component to acidic mineral component ranges from about 0.5:1 to about 80:1. The pre-mixed bone void filler composition may be in the form of a paste or putty, which is malleable, extrudable, and retains its shape during irrigation or handling in water or other physiologically compatible liquid carriers. The paste or putty may include additional components, e.g., those that improve retention of demineralized bone particles, improve extrudability, e.g., from a syringe, improve cohesiveness in water or other physiological compatible liquid carriers, improve moldability and/or improve shape retention during irrigation, or any combination thereof, relative to a paste or putty without the additional component(s). A paste or putty of the invention may be injected or introduced to a mold, or manipulated without use of a device. In certain embodiments, a paste or putty may have a more dynamic three-dimensional structure than a sponge.
Also described isa method for encouraging bone growth at a defect site. The method includes applying to the defect site a bone void filler composition in accordance with the various aspects of the invention. In one embodiment, a sponge, paste or putty of the invention may be employed alone or in combination, e.g., a sponge may be employed with a putty, or in conjunction with other implants, for restructuring or augmenting a defect. For example, a bone void filler composition that is applied in the method may be a sponge. In one embodiment, a bone void filler composition that is applied in the method may be a paste or putty formed by combining a particulated sponge with a liquid carrier. In one embodiment, a bone void filler composition that is applied in the method is a paste or putty that is formed by combining a rehydrated sponge of the invention with a liquid carrier and then with a biologically acceptable carrier. A paste or putty may be molded into a desired shape before being applied to a defect site, may be introduced to a cannulated device before being applied, e.g., injected into defect site, or may be manually shaped at the defect site.
Further, a bone void filler composition is described comprising: a three-dimensional composition comprising an acidic mineral component comprising a calcium source and a phosphate source or a lower alkyl carboxylate source, e.g., R-COO^- where R is (CH₃)(CH₂)_n where n is 0, 1, 2, 3 or 4; an osteoinductive component comprising demineralized bone comprising collagen; and an osteoconductive biologically acceptable carrier comprising a collagenous material, which is admixed with a collagenous biologically acceptable carrier to form a putty. In one embodiment, there is provided a kit for a bone void filler composition comprising: an acidic mineral component comprising a calcium source and a phosphate source or a lower alkyl carboxylate source; an osteoinductive component comprising demineralized bone comprising collagen; and a three-dimensional, osteoconductive biologically acceptable carrier component comprising a collagenous material; and instructions for preparing and/or using a sponge, paste or putty. The kit may further include a biologically acceptable carrier component comprising a liquid carrier.
The features and advantages of the present invention will be readily apparent to those skilled in the art.

BRIEF DESCRIPTION OF THE DRAWINGS

These drawings illustrate certain aspects of some of the embodiments of the present invention, and should not be used to limit or define the invention.

FIGURE 1 is a representation of a rat showing positions of the intramuscular implants.
FIGURE 2 depicts micro-CT scans obtained in studies evaluating bone growth from intramuscular implants in athymic rats.
FIGURE 3 is a representative image of rat ventral and dorsal views illustrating implant locations Q1-Q4 used in studies evaluating bone growth obtained from subcutaneous implants in athymic rats.
FIGURE 4 depicts micro-CT scans obtained in studies evaluating bone growth from subcutaneous implants in athymic rats.
FIGURE 5 depicts micro-CT scans obtained in studies evaluating bone growth from subcutaneous implants in athymic rats.
FIGURE 6 depicts micro-CT scans obtained in studies evaluating bone growth from subcutaneous implants in athymic rats.
FIGURE 7 depicts micro-CT scans obtained in studies evaluating bone growth from subcutaneous implants in athymic rats.
FIGURE 8 depicts micro-CT scans obtained in studies evaluating bone growth from subcutaneous implants in athymic rats.
FIGURE 9 depicts micro-CT scans obtained in studies evaluating bone growth from subcutaneous implants in athymic rats.
FIGURE 10 depicts histology results obtained in studies evaluating bone growth from subcutaneous implants in athymic rats. DM=demineralized matrix; MM=mineralized matrix from the original graft; RM=re-mineralized matrix with osteoclasts (OC), indicative of bone formation.
FIGURE 11 depicts vascularization results obtained in studies evaluating bone growth from subcutaneous implants in athymic rats.
FIGURE 12 depicts mineral density results obtained in studies evaluating bone growth from subcutaneous implants in athymic rats.
FIGURE 13 shows micrographs of the structure of an exemplary putty composition of the invention (100 x and 10 kx) versus a sponge composition of the invention (100 x and 10 kx).
FIGURE 14 illustrates exemplary shapes and dimensions of three-dimensional implants formed with bone void filler compositions of the invention. A) Implants with lips. B) Implants with concave receptacles. C) Capsule, bullet and sheet-shaped implants.
FIGURE 15 illustrates shapes with concave curves (e.g., for use inupper and lower dental ridge augmentation).
FIGURE 16 depicts representative radiographs of implants of DBM combined with various salts obtained at 4 weeks post subcutaneous implantation in athymic rats.
FIGURE 17 shows radiographs of rat left femur defects 4 weeks after filling with various compositions.
FIGURE 18 shows radiographs of sponge or putty implants of varying composition obtained at 4 weeks post subcutaneous implantation in athymic rats.
FIGURE 19 shows representative histology from samples from eight different groups (group number in upper left corner) at 8 weeks post defect filling stained with Mason's trichrome. BM=bone marrow; NB= new bone; OS=osteiod (newly mineralizing zone).
FIGURE 20 illustrates radiographs from rats 8 weeks after posterior-lateral spine fusions that employed a bone void filler composition of the invention or a composition having collagen and BMP-2.
FIGURE 21 illustrates sections from rats 8 weeks after posterior-lateral spine fusions that employed a bone void filler composition of the invention or a composition having collagen and BMP-2.
FIGURE 22 illustrates fluorochrome stained sections from rats 8 weeks after posterior-lateral spine fusions that employed a bone void filler composition of the invention or a composition having collagen and BMP-2.
FIGURE 23 illustrates serial sections from rats 8 weeks after posterior-lateral spine fusions that employed a bone void filler composition of the invention or a composition having collagen and BMP-2. Serial sections that were about 40 microns apart were stained with a fluorochrome or Trichrome.

DESCRIPTION OF EMBODIMENTS

The present invention relates generally to bone void filler compositions. Also described herein is the preparation of the bone void filler compositions, and the use of the bone void filler compositions in preventing or inhibiting bone loss and/or promoting bone growth. For instance, the present invention relates to bone void filler compositions containing an acidic mineral component, an osteoinductive component that contains demineralized bone, and a biologically acceptable carrier component as claimed in claim 1.
As described herein, the bone void filler compositions of the present invention have, as one (e.g., a "first") component, an osteoinductive component. As used in accordance with various embodiments of the present invention, "demineralized bone," or DMB, refers to bone that has been treated to remove an amount of the calcium phosphate mineral components sufficient to liberate (make more accessible) the endogenous bone growth factors. The level of demineralization of bone tissue is generally judged by the amount (wt %) of residual calcium found in the DMB. In general, "demineralized bone" refers to bone having less than about 8 wt % residual total calcium. The DMB useful in the compositions of the invention may be demineralized to have less than about 8 wt % residual calcium, less than about 4 wt % residual calcium, or between about 0.5 wt % to about 4 wt % residual calcium, or between about 0.5 wt % to about 2 wt % residual calcium.
Any demineralization processes known in the art, may be used to prepare DMB for use in the present invention. Demineralization is generally performed by exposing bone, from a mammalian, e.g., a human, source, to acidic solutions (e.g., HCl, acetic acid, or ethylene diamine tetracetic acid) with a pH less than about 4. The surface of the bone tissue is treated to remove a surface layer of its inorganic mineral, hydroxyapatite, leaving the structural properties of the organic phase of the bone constructs substantially unchanged. In some embodiments, the DMB may contain physiologically active levels of osteoinductive factors (e.g., bone morphogenetic proteins (BMPs)).
Demineralized bone may be provided as a powder, particulate, fiber or other form or may be provided in a matrix composition, "demineralized bone matrix (DBM)," where the powder, particles, and/or fibers may be combined with a liquid carrier to impart flowable or moldable properties to the composition. In particulate form, typical demineralized bone sources may have an average particle diameter of between about 105 microns and about 4 mm; between about 710 microns and about 2 mm; between about 200 microns and about 1 mm, between about 105 microns and about 500 microns; between about 105 microns and about 850 microns; or between about 250 microns and about 710 microns. In fiber form, typical demineralized bone sources may have an average thickness of between about 0.5 mm and about 15 mm and an average width of between about 2 mm and about 35 mm. The length of the fibers may vary from about 2 mm to about 300 mm.
Liquid carriers that can be used to prepare DBM include blood, blood components (e.g., plasma, serum or platelet rich plasma), bone marrow aspirate, normal or buffered saline, water, biocompatible liquids containing glycerol, lecithin, gelatin, hyaluronic acid, starch, or alginate, and/or other biocompatible liquids. The concentration of demineralized bone in DBM can be from about 10% to about 90% by weight (total weight including carrier).
The osteoinductive component of DMB is essentially the growth factors present in the DMB. Most of the osteoinductive factors are soluble at acidic pH. Hence, it is desirable that the growth factors are not extracted from the DMB during the acid demineralization process. DMB from cortical bone generally will have more osteoinductive factors than DMB from cancellous bone from the same source. Further, bone is known to contain inhibitors of bone formation (e.g., sclerostin).
The bone void filler compositions of the present invention may contain other components that have osteoinductive activity. Blood, blood components or bone marrow aspirate, when used in a composition, can contribute osteoinductive factors and/or osteogenic cells. Additionally osteoinductive factors such as recombinant or isolated bone morphogenetic proteins (e.g., BMP-2, BMP-7, GDF-5) may be added to the bone void filler compositions of the present invention.
Certain embodiments of the present invention may include freeze-dried demineralized bone. In some embodiments, the DMB may be freeze-dried to a point such that the freeze-dried bone has an average residual moisture of less than about 10 wt%, or less than about 5 wt%. In some embodiments, freeze-dried DMB may be rehydrated before use in preparing the bone void filler compositions of the present invention. Rehydrated freeze-dried DMB may have a residual moisture content of less than about 80 wt%, less than about 50 wt%, less than about 25 wt%, or between about 25 wt% and about 10 wt%, in certain embodiments.
The DMB may include more than one type of bone tissue (e.g., cancellous, cortical, or corticocancellous). The demineralized bone may include bone from a single donor source or from multiple donor sources. The demineralized bone may include materials from autogenic, allogenic or xenogenic sources (i.e., as compared to the DMB recipient).
As described herein, the bone void filler compositions of the present invention have, as another (e.g., a "second") component, an acidic mineral component. As used in accordance with various embodiments of the present invention, "acidic mineral component" refers to one or more components of the composition that provide an additional source of acidic mineral above and beyond any residual acidic mineral that might be present in the demineralized bone. The acidic mineral component provides local pH control and enhances the in vitro and/or in vivo efficacy of osteoinductive proteins. When combined with DMB or other sources of collagen, the acidic mineral component supplements local availability of essential bone components such as collagen, calcium, and phosphate. Moderately acidic microenvironments likely improve protein stimulated osteoinduction by enhancing the rates of protein solubilization and protein release from collagen. Supplementing the local concentration of soluble acidic mineral sources, such as Ca²⁺ and PO₄ ^3- ions, enhances the quantity and quality of bone produced, and increases rate of bone formation by reducing dependence on essential ion diffusion from serum and other body fluids.
The acidic mineral component of the present invention may contain a calcium containing source, a phosphate containing source or a lower alkyl carboxylate source, ceramic preforms, and/or other acidic minerals. "Contains," "comprise," "has," "having," or other similar language in the context of the "acidic mineral component" refers to the form in which the "acidic mineral component" is initially provided to the composition.
In one embodiment, the acidic mineral component has a calcium containing source and a phosphate source or a lower alkyl carboxylate containing source. The calcium source and the phosphate or lower alkyl carboxylate source may be present (e.g., provided) as a single compound or may be present as two or more compounds. For example, a single calcium phosphate present in the constituents used to make the bone void filler composition may be both the calcium source and the phosphate source. Alternatively, two or more compounds may be present in the constituents, where the compounds may include calcium, phosphate, or calcium and phosphate. Calcium and phosphate sources that may desirably be used in the mineral component of the present invention include monocalcium phosphate monohydrate [Ca(H₂PO₄)₂H₂O]; calcium hydrogen phosphate dihydrate [CaHPO₄2H₂O], amorphous calcium phosphate [Ca₃(PO₄)₂H₂O], anhydrous calcium hydrogen phosphate [CaHPO₄], partially dehydrated calcium hydrogen phosphate [CaHPO₄xH₂O, where x is between 0 and 2], tricalcium phosphate, including both α- and β- [Ca₃(PO₄)₂], tetracalcium phosphate [Ca₄(PO₄)₂O], octacalcium phosphate [Ca₈H₂(PO₄)₆5H₂O], and/or calcium pyrophosphate (Ca₂O₇P₂)[2CaO₂P₂O₅]. In one embodiment, anhydrous calcium hydrogen phosphate [CaHPO₄], partially dehydrated calcium hydrogen phosphate [CaHPO₄xH₂O, where x is between 0 and 2], and/or calcium hydrogen phosphate dihydrate [CaHPO₄2H₂O], which are collectively referred to herein as "DiCal", are employed in the compositions of the invention. In certain embodiments, where a calcium phosphate compound is employed, the ratio of calcium to phosphate (i.e., ratio of calcium cations to phosphate groups) of the compound ranges from about 0.5 to about 1. In certain embodiments, where a calcium phosphate compound is employed, the ratio of calcium to phosphate (i.e., ratio of calcium cations to phosphate groups) of the compound ranges from about 0.5 to about 2. In one embodiment, a calcium lower alkyl carboxylate such as calcium acetate may also be used as a soluble mineral component of the present invention. For instance, calcium acetate may be used alone or in combination with other phosphate sources, which include but are not limited to calcium hydrogen phosphate[CaHPO₄], monocalcium phosphate monohydrate [Ca(H₂PO₄)₂H₂O]; calcium hydrogen phosphate dihydrate [CaHPO₄2H₂O], amorphous calcium phosphate [Ca₃(PO₄)₂H₂O], anhydrous calcium hydrogen phosphate [CaHPO₄], partially dehydrated calcium hydrogen phosphate [CaHPO₄xH₂O, where x is between 0 and 2], tricalcium phosphate, including both α- and β-[Ca₃(PO₄)₂], tetracalcium phosphate [Ca₄(PO₄)₂O], octacalcium phosphate [Ca₈H₂(PO₄)₆5H₂O], and/or calcium pyrophosphate (Ca₂O₇P₂)[2CaO₂P₂O₅]; sodium dihydrogen phosphate (NaH₂PO₄), disodium hydrogen phosphate (Na₂HPO₄), trisodium phosphate (Na₃PO₄). In one embodiment, calcium acetate is employed in a composition of the invention. In one embodiment, a calcium lower alkyl carboxylate such as calcium acetate combined with anhydrous calcium phosphate [CaHPO₄], partially dehydrated calcium hydrogen phosphate [CaHPO₄xH₂O, where x is between 0 and 2], and/or calcium hydrogen phosphate dihydrate [CaHPO₄2H₂O], which are collectively referred to herein as "DiCal", are employed in a composition of the invention. In one embodiment, a calcium lower alkyl carboxylate such as calcium acetate combined with trisodium phosphate is employed in a composition of the invention. Calcium sources that may be used include, but are not limited to, calcium chloride [CaCl₂], calcium carbonate [CaCO₃], calcium oxide [CaO], calcium hydroxide [Ca(OH)₂], and the like. Phosphate sources that may be used include, but are not limited to, phosphoric acid [H₃PO₄], all soluble phosphates, and the like. The acidic mineral component may also contain sources of other minerals, including strontium, such as SrHPO₄ zinc, silicon, and/or magnesium. In one embodiment, the acidic mineral component may have a mineral other than (instead of) calcium, e.g., Sr, zinc, silicon or magnesium.
The form (e.g., crystals, particles, flakes, etc.) and size of the acidic mineral component may vary.
Compositions in accordance with the various embodiments of the present invention may contain additional agents to promote mineralization, including autograft, allograft or xenograft bone (e.g., cortical, cancellous or corticocancellous chips), bioceramics, biocomposites, proteins, lipids, and peptides.
Certain embodiment of the bone void filler compositions of the present invention also contain a biologically acceptable carrier component. The choice of biologically acceptable carrier component will depend on the form desired for the bone void filler compositions. In one embodiment, the biologically acceptable carrier component provides for a three-dimensional structure including the first and second components. In one embodiment, the biologically acceptable carrier component provides a three-dimensional, osteoconductive scaffold. In one embodiment, the three-dimensional, osteoconductive scaffold contains collagenous material, e.g., a scaffold formed of bovine collagen may contain other collagenous material, e.g., DMB particles may be a source of the other collagenous material. In one embodiment, the three-dimensional scaffold contains a polymer scaffold such as one prepared by weaving or electrospinning polycaprolactone (PCL), poly (D-, L-lactide) (PLA), polyhydroxybutyrate (PHB), chitosan, or a biocompatible, bioresorbable fiber as disclosed herein, e.g., instead of or in addition to a collagenous material.
In one embodiment, a bone void filler composition of the invention includes two different biologically acceptable carrier components, at least one of which provides for a three-dimensional structure. In one embodiment, a first biologically acceptable carrier component and a second biologically acceptable carrier component are mixed with an acidic mineral component, to form a slurry, and then DMB particles are added to the slurry, after which the resulting composition is added to a mold and subjected to freezing and lyophilization to form a dehydrated sponge. The dehydrated sponge may be rehydrated to form a putty.
In accordance with one group of embodiments of the present invention, which is subsequently described in greater detail, the compositions can be used in a rehydratable freeze-dried form, e.g., sponge, membrane, sheet, fleece, plug, rod, strip, etc. Such sponge may be mixed with additional components to form a putty or may, upon rehydration, form a putty. Sponges and putties are two embodiments and are used herein throughout as representative of other forms, e.g., pastes. Sponges may be stored in lyophilized form, frozen form or at temperatures from 15°C to about 30°C. Putties or pastes may be stored at temperatures from about 15°C to about 25°C.
In accordance with one group of embodiments of the present invention, which is subsequently described in greater detail, the compositions can be used as putties or pastes, e.g., in a malleable, moldable form (a dynamic three-dimensional structure). In one embodiment, a putty of the invention is prepared from a sponge by adding one or more biologically acceptable carrier components. In another embodiment, a putty of the invention is prepared by hydrating a lyophilized sponge that is formed by combining the first, second and third components discussed above with a collagenous biologically acceptable carrier component. In one embodiment, a pre-hydrated sponge, e.g., pre-hydrated with water, is prepared, provided or employed. In one embodiment, a bone void filler composition of the invention has putty like consistency and cohesiveness, has a fibrillar texture that may improve containment of DMB particles, has improved handling in water (e.g., decreased tendency to disintegrate) and/or provides for a three-dimensional structure that promotes better bone healing, e.g., as a result of the presence of the collagenous biologically acceptable carrier component. In one embodiment, a combination of biologically acceptable carrier components is present in the bone void filler composition of the invention, e.g., heat denatured collagen or heat denatured demineralized bone matrix and/or fibrillar collagen, and in one embodiment, the sources of collagen are the same.
In certain embodiments, "sponge" and "putty" compositions are adapted for use in making on-site preparations, e.g., preparations made at the time of an implantation procedure. For example, at the time of an implantation procedure, the sponge may be rehydrated with a suitable liquid carrier and then folded, molded or otherwise manipulated into a desired shape for use at a repair site. Alternatively, the sponge may be rehydrated with a suitable liquid carrier, excess moisture removed, and a collagenous biologically acceptable carrier component added and blended with the sponge to form a putty that is cohesive and malleable, which putty may be introduced to a repair site by a cannulated device (e.g., a syringe, needle, and/or cannula, and/or the like) or manually. In another embodiment, a lyophilized sponge may be rehydrated with a suitable liquid carrier which, after soaking, becomes a putty. Alternatively, the sponge may be particulated, either at the time of or prior to the implantation procedure. The particulated materials may then be combined with a suitable liquid carrier to form either a paste or putty. The liquid carriers that can be used to rehydrate the sponge or that can be combined with the particulate material to form a paste or putty, may be biological fluids, such as bone marrow aspirate, whole blood, blood components (e.g., serum, plasma, platelet rich plasma), etc., or other liquid carriers that include buffers, which may be desirable to buffer the composition to the physiological pH values of human serum (pH 7.1 to pH 7.4). Examples of buffers are known to those skilled in the art and include Tris and phosphate-buffered saline. More than one liquid carrier, for example, bone marrow aspirate and a buffering solution, may be used. The liquid carrier may include water, saline, glycerin, glycerol, lecithin, gelatin, hyaluronic acid, alginate, surfactants, carboxylic acids, dimethylsulfoxide, or tetrahydrofuran, or any combination thereof. Additionally, polymers such as aliphatic polyesters, polyethylene glycols, polyanhydrides, carboxylmethyl cellulose, hydroxymethyl cellulose, polysaccharides, dextran polymers, polymeric orthophosphates, or any combination thereof, may be used as the liquid carrier or be included in the composition.
As used in accordance with various embodiments of the present invention, "putty" refers to a dough-like/clay-like composition. "Paste," as used in accordance with various embodiments of the present invention, refers to a soft, moist, substance having a consistency between a liquid and a solid. A paste of the present invention is less solid than a putty and in some embodiments more solid that a gel, and in other embodiments may be injectable. As used in accordance with various embodiments of the present invention, "injectable" refers to the ability of certain bone void filler compositions of the present invention to be introduced at a repair site under pressure (as by introduction using a syringe or other cannulated device). An injectable composition of the present invention may, for example, be introduced between elements or into a confined space in vivo (e.g., between pieces of bone or into the interface between a prosthetic device and bone, into a tooth extraction socket, into alveolar ridge/sinus cavity, into a confined void with any geometry due to trauma created either natural or surgical procedure, into vertebral interbody spaces, spinal fusions, joint and trauma defects, bone fractures. An injectable composition may also be used to fill bone cysts, tumors and other well-delineated voids. A shaped composition may be used in spinal fusion, sinus lift, alveolar ridge augmentation, or a bone cavity (e.g., created by surgical procedure with regular geometry like a cylinder). Shaped compositions may also be designed as a circular sheet graft to be used in the acetabulum or a tubular graft to be used in the intramedullary space in primary and revision hip surgery or as a sheet that contours to the graft site to be used in fracture repair, bridge bone gaps or fragments, etc.
During application, the "putty" substance may be beaten or kneaded to the consistency of dough, and manipulated into a shape closely approximating that of the repair site. Pastes and putties provide ease of use and economy of product manufacture. Pastes and putties are desirable for surgical bone repair as they can be easily delivered to difficult surgical sites and molded in situ into desired shapes. These products are desirable for the reconstruction of skeletal defects, e.g., in spine, dental, and/or other orthopedic surgeries.
In one embodiment, the invention provides a malleable putty and the use of such a putty in bone grafting (e.g., joint revision) and surgical treatment of bony defects. In one embodiment, the putty comprises DMB particles, fibrillar collagen, an acidic mineral component (e.g., calcium phosphate dibasic (Dical)), and heat denatured collagen or gelatin as a collagenous carrier. The putty may be prepared by mixing fibrillar collagen, an acidic mineral component (e.g., calcium phosphate dibasic (Dical)), and an acidic solution (e.g., a hydrochloric acid containing solution) with DMB particles to form a mixture which is then lyophilized to form a sponge. The lyophilized mixture is then soaked in an aqueous liquid such as water, then gelatin or a heat denatured collagen or heat treated DMB particle containing solution is added to the rehydrated sponge (e.g., by injecting, spreading or soaking and gently blending with a spatula or by hand), so as to form a putty like material. For instance, a heat denatured collagen solution may be prepared by heating about 5% to about 30% (w/v), e.g., about 5% to about 15% or about 12% to about 30% (w/v), collagen in water or a saline (e.g., a 0.9% saline) solution at about 121°C for about 1 hour to about 3 hours in an autoclave to partially or mostly dissolve the collagen. The resulting viscous collagen solution is cooled to about 37°C to about 50°C and then may be used to make the putty. Gelatin, e.g., about 5% to about 30% (w/v), such as about 5% to about 15% (w/v), may be dissolved by heating. The dissolved gelatin may be maintained at about 37°C to about 50°C and then may be used to make the putty. Similarly, DMB particles may be heated in a saline solution to about 121°C for about 1 hour to about 3 hours in an autoclave to partially dissolve the DMB particles. The resulting DMB particle solution is cooled to about 37°C to about 50°C and then may be employed to prepare a putty. In one embodiment, the formulation includes a combination of fibrillar collagen and heat denatured collagen or gelatin or heat denatured DMB particles as a carrier to give putty-like flow and cohesiveness as well as a fibrillar three-dimensional structure which allows for molding into different shapes. The gelatin or heat denatured collagen may be from the same source as the fibrillar collagen or the gelatin may be produced by controlled acid hydrolysis (dilute HCl) of the fibrillar collagen followed by lyophilization to remove the acid.
In accordance with another embodiment of the present invention, which is subsequently described in greater detail, the bone void filler compositions can be used in a pre-mixed format, such as in the form of a paste or putty. Such pre-mixed, or ready-to-use, formulations have an advantage of requiring minimal preparation by the individual clinician or surgeon. The desired components of the paste or putty are dispersed in a liquid carrier to obtain a pre-mixed composition of a desired consistency. The liquid carriers that can be used to form the pastes or putties of this group of embodiments, may be selected from those liquid carriers described above for use in preparing the bone void filler compositions. In some embodiments, the liquid carriers contain biological fluids, such as bone marrow aspirate, whole blood, blood components (e.g., serum, plasma, platelet rich plasma), etc.
In accordance with the various embodiments of the present invention, the bone void filler composition may further contain a source of growth factor(s), e.g., bone morphogenetic proteins (BMPs). This source of growth factor(s) is in addition to any residual growth factor(s) that might be contained in the demineralized bone of the osteoinductive component. These additional growth factor(s) may come from blood, blood components or bone marrow aspirate used as a carrier.
BMPs are entrapped at high concentration within bone and are secreted by many bone-forming cell types. The primary function of BMPs is cellular signaling. Intracellular signaling occurs through the binding of a soluble growth factor to a specific cell receptor site. This signal pathway stimulates several different and important bone healing events, including the proliferation, migration, and differentiation of bone forming cells. The cells are, in turn, responsible for the synthesis of other proteins and growth factors that are important for regulating and controlling bone tissue formation. Although there is a vast array of BMPs described and known to one skilled in the art, BMP-2, -4, -6 and -7 are generally considered to be the most osteoinductive. Other growth factors, like TGF-betal, TGF-beta 3, and PDGF may also be used to stimulate bone formation.
In certain embodiments, there is provided a bone void filler composition having: an osteoinductive component containing DMB; an acidic mineral component; and a biologically acceptable carrier component having a three-dimensional, porous, osteoconductive scaffold. The porous scaffold may be open, interconnected, etc. In general, the relative amounts of each component may vary, e.g., according to differences in patient age, gender, health, systemic conditions, habits, anatomical location, etc. However, as will be explained in greater detail herein, particularly useful bone void filler compositions may be obtained with the use of specified ranges of the components.
In one embodiment, the use of a three-dimensional, osteoconductive scaffold allows the bone void filler composition to be produced in the form of a sponge. It is believed that a biologically acceptable, porous, three-dimensional scaffold restores function and/or regenerates bone by providing a temporary matrix for cell proliferation and extracellular matrix deposition with consequent bone in-growth until new bony tissue is restored and/or regenerated. The matrix may also provide a template for vascularization of this tissue. The scaffold may actively participate in the regenerative process through the release of growth factors, minerals and/or other substances beneficial to the bone formation process if such are present in the scaffold.
The macro and micro-structural properties of the scaffold influence the survival, signaling, growth, propagation, and reorganization of cells. They may also influence cellular gene expression and phenotype preservation. The following scaffold characteristics contribute to bone formation: cell biocompatibility; surface chemistry; biodegradability, porosity; and/or pore size.
In certain embodiments, the composition contains a collagenous material as the three-dimensional, porous, osteoconductive scaffold. Collagen is the main protein of connective tissue in animals and the most abundant protein in mammals. Bone is composed of strong, fibrillar bundles of collagen encased within a hard matrix including calcium phosphate predominately in the form of hydroxyapatite. Collagen is also a constituent in cartilage, tendon, ligament, and other connective tissues.
The collagen protein possesses a distinctive triple-helix tertiary structure of three polypeptide chains supercoiled about a common axis and linked by hydrogen bonds. At least nineteen distinct molecules have been classified as collagens, and specific types are associated with particular tissues. The solubility of collagen is affected by its conformation and extent of associations, whereby newly synthesized collagen chains are generally soluble but after formation of fibrils, they become essentially insoluble.
Collagen fibrils, referred to as fibrillar collagen, result from covalent cross-linking between the supercoiled chains by an enzymatic mechanism that strengthens and stabilizes the chains. Fibrillar collagen may be obtained from native sources such as human or animal dermis, tendon, cartilage or bone. It is generally recovered by proteolytically degrading natural collagen crosslinks to produce tropocollagen. Tropocollagen is soluble in acidic solutions (in one embodiment, between pH 3 to pH 4). These solutions can be cleaned and purified prior to collagen fiber reassembly by pH neutralization. Fibrillar collagen is generally less dense, less soluble, and swells more in solution than non-fibrillar collagen. Fibrillar collagen may be prepared by any method, including those disclosed in Rubin et al., Biochemistry, 4:181 (1965); Helseth et al., Biol. Chem., 256:7118 (1981); Capaldi et al., Biopolymers, 21:2291 (1982) and Gelman et al., J. Biol. Chem., 254:11741 (1979). For example, a tissue source having collagen may be repetitively treated by mechanically removing contaminants, such as fat, and washing the mechanically treated materials in an alkaline solution, e.g., such as one that yields chlorine, which optionally also contains an anti-microbial agent. The washed material may be frozen and freeze dried prior to milling. In one embodiment, fibrillar collagen useful in the bone void filler compositions of the invention, has cross-links found in native tissue, which provides for a native three-dimensional structure. In one embodiment, fibrillar collagen useful in the bone void filler compositions of the invention is greater than about 90 wt% Type I collagen, e.g., about 95 wt% Type I collagen, which fibrillar collagen preparation may contain less than about 10 wt% Type III collagen, e.g., less than about 5 wt% Type III collagen.
Due to its high degree of biocompatibility with the human body, collagen has been successfully used in a variety of medical and dental applications for many years with minimal adverse responses. During its manufacture, potentially antigenic portions of the collagen molecule may be removed, resulting in a product that is highly biocompatible and well-tolerated by the tissue (e.g., atellopeptide collagen). Collagen is also chemotactic for fibroblasts and other cells involved in bone tissue repair. Collagen biocompatibility ensures that the products are well integrated in the host tissue without eliciting an immune response.
Collagenous materials used in the bone void filler compositions of the present invention may be from any source as long as they are capable of being used to form the implantable material. These include natural collagen sources such as mammalian, e.g., human, tissues, and synthetic collagen sources manufactured using recombinant technologies. The collagenous material may also contain gelatin. The collagen may be of any type (e.g., collagen Types I, II, III, or X and/or gelatin). In various embodiments, the collagen may be derived from bovine, porcine, equine, or ovine dermis or connective tissue. Bovine dermal collagen from Devro Medical and bovine tendon collagen from Collagen Matrix are acceptable collagens in certain embodiments. Type I collagen derived from tendon, fascia or bone may also be used. These tissues can be allogeneic or xenogeneic, such as from bovine, porcine, equine, or ovine sources. Soluble collagen, insoluble collagen, or combinations of soluble and insoluble collagen may be used as long as a sponge can still be obtained. Acids used to render collagens soluble, if not removed from the final bone void filler compositions of the present invention, may affect the stability of the compositions over time if the compositions are moist or wet. However, lyophilization results in the complete or partial removal of the acids used to solubilize collagen, greatly reducing any possible instability in certain embodiments. Nonetheless, in other embodiments, soluble collagen, if used as part of the carrier, may be subjected to steps to remove any residual acid followed by reconstitution.
The surface chemistry of the scaffold can control and affect cellular adhesion. It can also influence the solubility and availability of proteins essential for intracellular signaling. Intracellular signaling maximizes osteoinductivity through controlled cellular differentiation, proliferation, and stimulation.
Collagen also provides a favorable extracellular matrix for bone forming cells, e.g., osteoblasts, osteoclasts, osteocytes, etc. The natural affinity of bone forming cells for the collagen matrix has been demonstrated to favorably influence the function and signaling required for normal cellular activity.
The degradation rate of the scaffold desirably approximates the bone-forming rate. Slower degradation rates can hinder the rate of remodeled, load-bearing bone formation. Faster degradation can result in unhealed defects. The solubility and resorption of collagen is affected by its conformation and the degree of collagen cross-linking. The in vivo solubility and resorption of collagen is also influenced by the local concentration of proteolytic agents and vascularity at the site.
In order to form a more stable sponge structure, collagen from some sources may benefit from crosslinking before use. In one embodiment, collagens that do not require crosslinking following combination with the osteoinductive component are used. In embodiments where a crosslinked collagen is employed, the collagen may be crosslinked to control the solubility and the extent and rate of collagen resorption and improve the mechanical properties, e.g., tensile strength and elasticity. Collagen crosslinking may occur by various methods, such as dehydrothermal (DHT), UV light exposure, and chemical crosslinking with aldehydes (e.g., glyceraldehyde, formaldehyde, and glutaraldehyde), carbodiimides and various amino acids. The crosslinking conditions may typically preserve the in vivo lifetime of the bone void filler composition for up to about twelve weeks, allowing the collagen to function as a scaffold for bone healing, in contrast to noncrosslinked collagen containing compositions which may have an in vivo lifetime from 1 to 3 weeks. Collagen is eventually degraded by host enzymes in the surrounding tissue.
Scaffolds with high porosity and interconnectivity are generally desired. Scaffolds desirably possess an open pore, fully interconnected architecture to allow homogeneous and rapid cell in-growth, and facilitate vascularization of the construct from the surrounding tissue. To this end, the total pore volume porosity of the scaffold desirably simulates that of cancellous bone. Cancellous bone is a highly porous structure (about 50 vol. % to about 90 vol. %) arranged in a sponge-like form, with a honeycomb of branching bars, plates, and rods of various sizes called trabeculae. In one embodiment of the present invention, the scaffold desirably ensures pore interconnectivity to allow for the diffusion of nutrients and gases and for the removal of metabolic waste resulting from the activity of the cells within the scaffold. Smaller pores may occlude and restrict cellular penetration, matrix production, and tissue vascularization. Larger pores may detrimentally influence the mechanical properties of the structural scaffold. In one embodiment, pore size may ranges from about 1 µm to about 5 mm. In one embodiment, pore size may range from about 10 µm to about 5 mm. In one embodiment, pore size may range from about 10 µm to about 1 mm. In one embodiment, porosity ranges are from about 30 vol.% to about 90 vol. %
In some embodiments, the DMB source may also be the source of the collagenous material. Such collagenous materials that may also be a source of demineralized bone include commonly available DMBs, e.g., from Allosource Inc., RTI Biologics, Osteotech Inc., e.g., DMB without a carrier. In such embodiments, to obtain a composition of a desired consistency it may be necessary to add a liquid carrier.
Other acceptable three-dimensional, osteoconductive scaffolds that can be used in accordance with embodiments of the present invention may be prepared from materials including: (i) biologically derived (e.g., silk, cellulose, starch) and synthetic biodegradable polymers/copolymers scaffolds (e.g., PLA/PGA, PCL, and/or PHB, for instance, formed as a bead or a woven scaffold); (ii) biocompatible, bioresorbable fibers, such as glass fibers; and (iii) other biodegradable matrices, such as biodegradable metals (Mg based preforms).
In addition to the biologically acceptable carrier component having a three-dimensional, open-porosity, osteoconductive scaffold, the bone void filler compositions in accordance with embodiments of the present invention also contain an osteoinductive component containing DMB and an acidic mineral component, which have been previously described herein. In accordance with this embodiment, exemplary acidic mineral components contain DiCal.
In accordance with certain of embodiments of the present invention, the relative concentrations of osteoinductive component containing DMB, acidic mineral component, and three-dimensional, porous, osteoconductive scaffold component may be optimized for a particular clinical application. Notwithstanding the foregoing, particularly useful bone void filler compositions in accordance with certain embodiments are obtained by using specified ranges of the components. Specifically, the inventors have found that certain ratios of acidic mineral component relative to the amount of collagen, as biologically acceptable carrier, provide unexpected increases in bone growth potential. In certain embodiments, an acidic mineral component (e.g., DiCal), is used in the range of about 1 % to about 60 % by weight relative to the combined weight of acidic mineral component and the total weight of collagen, accounting for collagen contained in the carrier as well as any collagen found in other components, including the DMB, which was assumed for purposes of experimentation to be 90% by weight collagen. In some embodiments, the acidic mineral component is used in the range of about 1 % to about 50 %, from about 1 % to about 30 %, from about 1 % to about 20 %, and from about 1 % to about 10 %. In certain embodiments, calcium acetate as a mineral component alone or calcium acetate combined with a phosphate salt (e.g., calcium hydrogen phosphate and trisodium phosphate) is used in the range of about 1 % to about 60 % by weight relative to the combined weight of mineral salt and the total weight of collagen, accounting for collagen contained in the carrier as well as any collagen found in other components, including the DMB, which was assumed for purposes of experimentation to be 90% by weight collagen. In some embodiments, the mineral component is used in the range of about 1 % to about 50 %, from about 1 % to about 30 %, from about 1 % to about 20 %, and from about 1 % to about 10 %.
Effective mass ratios of a DMB component to acidic mineral component, as determined in rat ectopic assays, range from about 0.5:1 to about 80:1. In some embodiments, effective mass ratios of DMB component to acidic mineral component range from about 1:1 to about 40:1, from about 1:1 to about 16:1, from about 1:1 to about 8:1, from about 5:1 to about 9:1, and from about 1:1 to about 4:1. In some embodiments, the dry weight percentages of the acidic mineral component (e.g., DiCal) range from about 0.5% to about 60%, the osteoinductive component (e.g., DMB) range from about 35% to about 90%, and the carrier component (e.g., collagen) range from about 3.5% to about 30%. In some embodiments, the dry weight percentages of the acidic mineral component (e.g., DiCal) range from about 9% to about 40%, the osteoinductive component (e.g., DMB) range from about 55% to about 90%, and the carrier component (e.g., collagen) range from about 5% to about 30%. In some embodiments, the dry weight percentages of the acidic mineral component (e.g., DiCal) range from about 9% to about 25%, the osteoinductive component (e.g., DMB) range from about 70% to about 90%, and the carrier component (e.g., fibrillar collagen) range from about 5% to about 20%. In one embodiment, the DMB to DiCal ratio is about 7 to about 8. In one embodiment, the volume (mL) of acid solution, e.g., 30 mM HCl, per mass (g) of collagen is about 33 to about 35.
Processes for producing bone void filler compositions in accordance with one embodiment of the invention in the form of sponges, and subsequently producing pastes or putties, e.g., from particulated sponge, are not generally limited and include those methods known in the art. In one method, an acid solution, e.g., a hydrochloric acid containing solution, is added to collagen to wet the collagen. Acidic mineral, e.g., DiCal, is added and the combination is mixed thoroughly with a spatula. The combination is then whipped with a lab scale mixer to obtain a composition with a gel-like consistency. As used in the present invention, the term "gel" generally refers to a jelly-like, thick, soft, partly liquid substance. In general, a gel may be extruded without substantial mechanical deterioration through at least a 13 gauge syringe needle. DMB powder is then added to the collagen-acidic mineral gel and mixed with a spatula to form a collagen-acidic mineral-DMB dispersion. In one embodiment, DMB particles are added simultaneously with collagen, mineral and acid solution. The sponge is obtained from a process in which the collagen-acidic mineral-DMB dispersion is placed in a mold of a desired shape and thereafter frozen and lyophilized. The sponge may be cast in any desired shape, including strips, discs, sheets, bullets, cylinders, wedge, trough, anatomic shapes such as an alveolar ridge, etc. The types of collagen that may be used are described above and include bovine dermal fibrillar collagen.
In one method, collagen (e.g., fibrillar), acidic mineral (e.g., DiCal) and DMB (e.g., particles) are simultaneously added to an acidic solution (e.g., a hydrochloric acid solution) and whipped with a lab scale mixer to obtain a composition. The collagen-acidic mineral-DMB composition is placed in a mold of a desired shape and thereafter frozen and lyophilized to form a sponge. The sponge may be cast in any desired shape, including strips, discs, sheets, bullets, cylinders, etc. The types of collagen that may be used are described above and include bovine dermal fibrillar collagen.
In one method, hydrochloric acid is added to collagen and gelatin. An acidic mineral, e.g., DiCal, is added to that mixture and the combination is mixed thoroughly with a spatula. The combination is then whipped with a lab scale mixer to obtain a composition. DMB powder is then added to the collagen-gelatin-acidic mineral composition and mixed with a spatula. The collagen-gelatin-acidic mineral-DMB composition is placed in a mold of a desired shape and thereafter frozen and lyophilized to form a sponge. The sponge may be cast in any desired shape, including strips, discs, sheets, bullets, cylinders, etc. The types of collagen that may be used are described above and include bovine dermal fibrillar collagen.
As indicated, preparation of the bone void filler compositions in accordance with some embodiments may involve freezing and lyophilization. In certain such embodiments, the composition may be frozen at -20 to -80 °C for about two hours. Freezing may be conducted in a single or multiple steps. In certain such embodiments, the composition may be lyophilized for at least about sixteen hours. In other embodiments, the composition may be lyophilized for at least about 48 hours.
After lyophilization, the bone void filler composition, now in the form of a rectangular sponge or other desired shape, may be subjected to crosslinking. Crosslinking may be accomplished by a variety of methods known to one skilled in the art, including but not limited to dehydrothermal (DHT) crosslinking, UV light exposure, and chemical crosslinking with aldehydes (e.g., glyceraldehyde, formaldehyde, and glutaraldehyde), carbodiimides and various amino acids. In DHT crosslinking, the composition is placed in a vacuum oven chamber, the chamber is evacuated to create a vacuum, and the composition is heated for a period of time. In one embodiment, the composition is heated to about 110 °C. In one embodiment, the composition is heated in a vacuum oven for about 48 hours.
Following freezing, lyophilization, and any optional crosslinking, the solid composition can be, as has been previously described, in the form of a sponge. The sponge may be combined with a liquid carrier, as previously described, and then manipulated, e.g., molded, into a desired shape and applied to a defect site. In one embodiment, the sponge may be rehydrated and an additional collageneous biologically acceptable carrier added thereto to obtain a paste or putty of a desired consistency. In one embodiment, the carrier comprises gelatin, denatured DMB and/or collagen, which carrier may bind to a fibrillar collagen structure (e.g., one found in a rehydrated sponge). A collagenous carrier may be prepared by heating collagen, e.g., from about 5% to about 15% (w/v) or about 10 to 30% (w/v) collagen, in an aqueous solution, e.g., saline (e.g., 0.9% w/v) to over 100°C (e.g., about 121°C) for about an hour. A gelatin containing carrier solution may be prepared by dissolving gelatin powder in an aqueous solution (e.g., water) to about 5 to about 15% (w/v) gelatin. Dissolved or partially solubilized carriers may be maintained at about 37°C to about 50°C prior to putty or paste formation. For example, a sponge is rehydrated with a liquid carrier and excess moisture is removed, then a carrier is added and blended to form a putty that may be packed into a container or introduced to a delivery device (e.g., syringe) or dehydrated. In one embodiment, the carrier that is added to the rehydrated sponge is from the same source as the collagen in the sponge but is heat denatured. In one embodiment, the source of carrier in the sponge and the subsequently added carrier are different. In one embodiment, a putty of the invention includes two or more types of carrier, e.g., a combination of fibrillar collagen and gelatin.
Alternatively, the sponge may be particulated, shredded or otherwise disaggregated as previously described and then combined with a liquid carrier, as previously described, to obtain a paste or putty of a desired consistency. Methods of forming particles are known to one skilled in the art and include, but are not limited to, grinding, milling, chopping, and/or molding. In certain embodiments, particles are formed by milling the solid composition. Milling may occur using a Wiley mill (Thomas Scientific, Swedesboro N.J.). The mesh size on the mill directs the size of the resultant particles. In one embodiment, a -20/+140 meshes are used that creates particles in the range of about 100 µm to about 840 µm. The particles may be sized, for example, by sieving. At any point in the process, additional components may be added to the composition, as described above, including bulking agents (e.g., bone chips).
The bone void filler compositions of the invention may be prepared under sterile conditions and/or using sterile components, and/or sterilized once a sponge, paste or putty is obtained, e.g., to reduce or eliminate the introduction of microbes including viruses upon implantation. In one embodiment, a sponge, paste or putty of the invention or individual components thereof is subjected to irradiation, e.g., gamma irradiation, for instance 30 kGy, at low temperatures, and/or in an inert environment, or low dose electron beam (E beam), or chemical sterilization, e.g., using ethylene oxide or gas plasma.
The on-site preparations that are obtained in accordance with the one embodiment of the present invention have the advantage of allowing the clinician to vary the concentrations and quantities of bone void filler composition (sponge or particulates) and liquid carrier to obtain desired handling characteristics. On-site preparation also permits the addition of optional components at the discretion of the clinician.
The bone void filler compositions in accordance with certain embodiments desirably have a pH as delivered to the defect site of from about 2 to about 7, e.g., from about 3 to about 5 or from about 5 to about 7. It has been found that when the pH is within the limitations identified above, the materials have excellent physical properties, such as a putty consistency which is elastic and dough-like (see e.g., US20080293617 , US20060246150 and US20080152687 ). At higher pH, the materials may become crumbly with the consistency of wet sand. A putty consistency is desired because it provides many benefits such as enhanced cohesiveness, ease of handling and moldability. Because materials of the present invention are cohesive, they are also believed to provide the benefit of maintaining an active compound at the site of implantation longer than comparative materials with less cohesiveness.
The bone void filler composition may be provided as a kit. Acceptable kits may include one, two, three or four receptacle-containers, one of which may be suitable for combination and/or "hydration" of the components. In one such embodiment, the kit includes the particulated bone void filler composition described above. The kit may further have a mixing implement such as a spatula, stir rod, etc., a disposable syringe barrel with or without a cannulated extension (e.g., a needle) in which to place and deliver the mixed paste, one or more instruements for implanting the composition, instructions for formulating and/or using the composition, etc.
As previously taught herein, in accordance with one embodiment, a bone void filler composition is provided in the form of a pre-mixed paste or putty. The bone void filler compositions of this group of embodiments thus contain an osteoinductive component containing DMB; an acidic mineral component; and a liquid carrier as a biologically acceptable carrier component. The relative amounts of each component may be optimized for a particular clinical application, which may vary according to differences in patient age, gender, health, systemic conditions, habits, anatomical location, etc. However, as will be explained in greater detail herein, the present inventors have found that particularly useful bone void filler compositions are obtained with the use of specified ranges of the components.
The bone void filler compositions of one of the embodiments of the invention are prepared using a liquid carrier. The liquid carriers that can be used to form the pastes or putties of this embodiment of the present invention may be selected from those liquid carriers previously described for use in preparing the bone void filler compositions. As previously described, these liquid carriers are desirably biological fluids, such as bone marrow aspirate, whole blood, blood components (e.g., serum, plasma, platelet rich plasma), etc. Other liquid carriers may include buffers, which may be desirable to buffer the composition to the physiological pH values of human serum (pH 7.1 to pH 7.4), e.g., before combining with an acidic mineral component. Examples of buffers are known to those skilled in the art and include Tris and phosphate-buffered saline. More than one liquid carrier, for example, bone marrow aspirate and a buffering solution, may be used. The liquid carrier may include water or saline, and components such as solubilized collagen, glycerin, glycerol, lecithin, surfactants, carboxylic acids, dimethylsulfoxide, and/or tetrahydrofuran. Collagen is commonly solubilized using an acid treatment. When solubilized collagen is employed as a liquid carrier, it may be desirable to remove any residual acid present in the collagen. Additionally, natural and synthetic polymers such aliphatic polyesters, polyethylene glycols, polyanhydrides, dextran polymers, and/or polymeric orthophosphates may be included in the composition. The carrier may also be prepared using other materials including biologically derived (e.g., silk, cellulose, starch) and synthetic biodegradable polymers/copolymers (e.g., PLA/PGA, PCL, PHB). In one embodiment, the liquid carrier may promote cellular infiltration and retain the composition at the defect site, without being cytotoxic. The liquid carrier may promote such cellular infiltration by providing a molecular matrix for cell migration.
In accordance with this embodiment, exemplary acidic mineral components contain DiCal. Particularly useful pre-mixed bone void filler compositions are obtained with the use of specified ranges of the components. Specifically, effective mass ratios of demineralized bone component to acidic mineral component range from about 0.5:1 to about 80:1. In some embodiments, effective mass ratios of demineralized bone component to acidic mineral component range from about 1:1 to about 40:1, from about 1:1 to about 16:1, from about 1:1 to about 8:1, from about 5:1 to about 9:1, and from about 1:1 to about 4:1. In some embodiments, ratios of acidic mineral component relative to the amount of demineralized bone matrix collagen range from about 2.5:1 to about 7.5:1 provide unexpected increases in bone growth potential.
Processes for producing bone void filler compositions in accordance with this embodiment of the invention in the form of pastes or putties are not generally limited and include those methods known in the art. In one embodiment, a number of components including DMB and acidic mineral components are combined with a sufficient quantity of liquid carrier to achieve a bone void filler composition of a desired consistency, e.g., a paste or putty. Alternatively, a sponge is combined with a collagenous carrier which is suspended or dissolved in a liquid, to achieve a bone void filler composition of a desired consistency, e.g., a paste or putty. As a putty or paste, the composition desirably has suitable rheological properties (e.g., viscosity) so as to be injectable through applicators including large gauge applicators, such as catheters, or syringes, while largely remaining at the implant site.
The bone void filler compositions in accordance with this embodiment desirably have a pH as delivered to the defect site of from about 2 to about 7, e.g., from about 3 to about 5 or from about 5 to about 7. It has been found that when the pH is within the limitations identified above, the materials have excellent physical properties, such as a putty consistency which is elastic and dough-like. At higher pH, the materials may become crumbly with the consistency of wet sand. A putty consistency provides many benefits such as enhanced cohesiveness, ease of handling and moldability. Because materials of the present invention are cohesive, they are also believed to provide the benefit of maintaining an active compound at the site of implantation longer than comparative materials with less cohesiveness.
In accordance with bone void filler compositions of the present invention, there is also provided methods for using the bone void filler compositions to promote bone growth. In accordance with such embodiments, the bone void filler composition, in the desired form, is applied to a desired anatomical site of the patient, e.g., the bone defect site. Bone void filler compositions in accordance with the present invention in the form of a sponge are combined with a liquid carrier, premolded or molded or otherwise formed into a desired shape generally conforming to the shape and size of the defect site, and then positioned adjacent or pressed, either manually and/or using instrumentation, into the defect site. Bone void filler compositions in accordance with the present invention in the form of a putty, either resulting from the combination of particulated sponge and a liquid carrier or a ready-to-use putty, are molded or otherwise formed into a desired shape generally conforming to the shape and size of the defect site, and then positioned adjacent to or pressed, either manually and/or using instrumentation, into the defect site. Bone void filler compositions in accordance with the present invention in the form of a paste, either resulting from the combination of particulated sponge that has been combined with a liquid carrier or a ready-to-use paste, are applied to the defect site. If the paste is injectable, the paste may be loaded into the barrel of a disposable syringe, with or without a cannula (e.g., needle) attached, and is extruded through the barrel aperture to the desired anatomical site.
In accordance with the methods of the invention, a defect site is desirably prepared to expose healthy bleeding bone, facilitating subsequent bone growth. The methods may be performed using minimally invasive procedures known to one skilled in the art. The methods may be used in at least partially filling bone voids and/or gaps of the skeletal system. Such applications include induction of bone formation for hip replacement operations, knee replacement operations, spinal fusion procedures, repair of periodontal defects, treatment of osteoporosis, repair of bone tumor defects, dental procedures, repair of cranial maxilla facial defects, and repair of bone fractures or defects. These voids and/or gaps may be a result of a development failure, degeneration or trauma, either natural or by surgical creation. The bone void filler composition is resorbed by the body during the healing process (over days, weeks, and months).
The invention will be further described by the following non-limiting examples.

Example 1

Intramuscular Implant Evaluations

To determine if the addition of DiCal would enhance bone growth in implanted DBM containing compositions, various test samples, as described below were implanted intramuscularly in athymic rats. Surgery on each rat was performed as follows. Prior to the surgery, the rats were anesthetized by intraperitoneal injection of ketamine/Xylazine solution; 70 mg/kg of ketamine and 5 mg/kg of xylazine. General anesthesia was noted by a lack of response to a toe pinch. Anesthesia was maintained with isoflurane, if needed.
The skin over the semitendinosus muscle was shaved (if necessary) using an electric clipper and prepared with chlorhexadine and alcohol scrub. The rat was placed in lateral recumbency. Using a scalpel or scissors, a 1 cm incision was made in the skin in line with the long bone. Two 2 mm incisions were made in the semitendinosus muscle and blunt dissection used to prepare the implant bed.
Using aseptic technique, each test sample allocated for intramuscular implantation was placed in the semitendinosus muscle. A few drops of sterile saline were used, as necessary, on the implantation site before inserting the implant to assist in placement of the test sample at the placement site. The rat was then repositioned to the other side and the procedure repeated. Each opening was closed with appropriate suture and skin wound closure was completed using stainless steel wound clips. Figure 1 is a representation of a rat showing positions of the intramuscular implants.
Puros® DBM was used as the carrier and the source of DMB for all systems evaluated in this example. Four different systems were evaluated: system 1(a) containing Puros® DBM (25 mg); system 1(b) containing Purest DBM (25 mg) and BMP-2 (10 micrograms); system 1(c) containing Puros® DBM (12.5 mg) and DiCal (12.5 mg); and system 1(d) containing Puros® DBM (12.5 mg), DiCal (12.5 mg) and BMP-2 (10 micrograms). For systems containing DiCal, DiCal was employed in a 1:1 ratio (i.e., DiCal dry wt.: Puros® DBM wet wt.) and a 2500:1 ratio (i.e., DiCal dry wt.:BMP-2 dry wt.). The samples were generally prepared as follows. The components were combined (e.g., the DiCal was mixed with the wet Puros® DBM putty) by hand using a spatula so as to evenly distribute the components. The compositions were then subjected to freezing conditions at -80°C for 30 minutes. Thereafter, the compositions were subject to lyophilization for at least 24 hours. 25 mg of each sample system was then placed into gelatin capsules and implanted intramuscularly as described above.
After 28 days, tissue containing each implant was removed for evaluation, including micro-CT scans. For the micro-CT evaluations, these explants were fixed in formalin. The micro-CT scans are depicted in Figure 2 and data derived therefrom in Table 1. The micro-CT scans and derived data show that the presence of DiCal markedly enhanced bone formation in systems with BMP (e.g., an approximately 83% increase in total bone mineral deposition).

The data in Table 1 summarizes the bone volume, bone mineral density and bone volume/total volume for the four groups. As expected, bone volume and the ratio of bone volume (mineralized)/total volume increased when BMP-2 was added (compare 1(a) and 1(b), and 1(c) and 1(d)). The ratio of bone volume/total volume also increased when DiCal was added (about 3 fold; compare 1(a) to 1(c)), although not to the same extent as BMP-2 containing compositions. While only one concentration of DiCal was tested, the results in Table 1 indicate that DiCal provides for an increased ratio of mineralized bone volume/total volume in the absence of exogenous BMP-2.

Table 1

System	Bone Volume (mm³ ± SD)	Bone Mineral Density (mg hydroxyapatite/cc ± SD)	Bone Vol/Total Vol ± SD
1(a)	2.65 ± 3.06	565 ± 124	0.03 ± 0.02
1(b)	31 ± 15	454 ± 17	0.375 ± 0.08
1(c)	2.65 ± 1.94	512 ± 41	0.10 ± 0.15
1(d)	52± 33	496 ± 27	0.198 + 0.11

Example 2

Subcutaneous Implant Evaluations

Various systems, as described below, were implanted subcutaneously in athymic rats to evaluate the compositions with respect to their efficacy for bone growth. Male athymic rats, about seven weeks old at the commencement of the study, were used. Surgery on each rat was performed as follows. Prior to the surgery, the rats were anesthetized by intraperitoneal injection of ketamine/Xylazine solution; 70 mg/kg of ketamine and 5 mg/kg of xylazine. General anesthesia was noted by a lack of response to a toe pinch. Anesthesia was maintained with isoflurane, if needed.
The ventral and dorsal thoracic area of each rat was swabbed with chlorhexadine and alcohol scrub. Using a scalpel or scissors, a 1 cm incision was made in the skin on the right side. This ventral incision was made at the base of the rib cage. After incision, a pocket was prepared beneath the skin and above the incision by blunt dissection towards the axilla. A large blood vessel (cranial thoracodorsal vein) was noted which was often adhered to the skin/subcutaneous tissues. The right ventral implant was placed in the pocket of the subcutaneous tissue approximately 5 mm anterior to the incisions on the chest wall directly below the cranial thoracodorsal blood vessel. When the right ventral side was implanted, the left side had the same procedure done for implantation. The rat was then repositioned to make two more small (1 cm) incisions in the skin of the dorsal thorax. The two dorsal implants were placed toward the middle of the rib cage. All wound closure was accomplished using either stainless steel wound clips or sutures. Thus, each rat had four subcutaneous implants with bilateral placements of the test articles in each of the ventral and dorsal thoracic regions. Figure 3 is a representative image of a rat ventral and dorsal views depicting subcutaneous implant sites Q1-Q4.
Three different types of systems were evaluated: implants containing collagen and DMB, implants containing collagen, DMB, and BMP-2, and implants containing collagen, DMB, and varying amounts of DiCal. Nominal DiCal concentrations evaluated were 11, 33, 50, and 60 weight percent relative to the combined weight of acidic mineral component and the total weight of collagen, accounting for collagen contained in the carrier as well as any collagen found in other components, including the demineralized bone, which was assumed for purposes of experimentation to be 90% by weight collagen. Two lots of the same DMB, were provided by RTI Biologics, Inc.
Implants were generally prepared as follows. Hydrochloric acid (30 mM) was added to the collagen to wet the collagen. The combination was then whipped with a lab scale mixer to obtain composition with a gel-like consistency. The appropriate amount of DMB powder was added and mixed thoroughly with a spatula to obtain a putty-like consistency. Discs of a desired shape residing on a glass plate were filled with the putty. A second glass plate was positioned over the discs and clamped into place. The glass plate assembly was frozen, generally for a minimum of one hour at -80 °C. The discs were removed from the freezer and excess material was trimmed from the disc molds. The glass plate assembly was quickly returned to the freezer again for a minimum of one hour at -80 °C. The assembly was then subjected to lyophilization for a minimum of 12 hours. The individual, now sponge, implants were then recovered from the molds.
For implants intended to contain DiCal, the appropriate amount of DiCal was added to the combination of hydrochloric acid and collagen prior to the whipping step. The combination of collagen, hydrochloric acid, and DiCal was first mixed with a spatula and then whipped with a mixer.
For implants intended to contain BMP-2, 20 µL of reconstituted BMP-2 was added to one side of the lyophilized sponge implant disc. The BMP-2 solution was allowed to soak into the sponge implant disc. The sponge implant disc was subjected to freezing conditions for one hour at -80 °C. The assembly was then subjected to lyophilization for a minimum of 12 hours. The individual, now sponge, implants were then recovered. Then, 20 µL of reconstituted BMP-2 was added to the other side of the sponge implant disc and the procedure was repeated.
After 21 days, the implants were removed for evaluation, including micro-CT and histological evaluation. The explants were fixed in 10% NBF and radiographed. Following radiography, the samples were subjected to micro-CT. The micro-CT scans are depicted in Figures 4-9. Each group of micro-CT scans in Figures 4-9 depict explants taken from various locations Q1-Q4 of various test subjects. The CT -scans show that the presence of DiCal enhanced bone formation at each of the concentrations evaluated. Histological analysis showed that the presence of DiCal also resulted in increased vascularization. Figure 10 is representative and shows that an implant containing collagen, DMB, and 11% DiCal showed increased vascularization and the activation of both osteoclasts and osteoblasts compared to an implant containing only collagen and DMB. In addition, Figure 11 shows a marked increase in vascularization at DiCal concentrations ranging from 11 % - 60%. Moreover, Figure 12 demonstrates, for similarly prepared samples, the mineral density enhancement associated with the addition of DiCal concentrations ranging from 1.23% to 20%.

Example 3

Exemplary Putty Composition Preparation

In this example, gelatin was combined with fibrillar collagen, a source of calcium and phosphate and DMB particles to form a putty. A demineralized bone matrix sponge was prepared by whipping 0.18 gram of collagen, 7.3 mL 30 mM hydrochloric acid, 0.21 gram calcium phosphate dibasic (Dical), and 1.6 gram demineralized bone particle into a slurry, followed by lyophilization of the slurry into a 5 cm by 2 cm by 0.5 cm sponge. A 12% w/v gelatin solution was prepared by adding 1.2 gram gelatin into 10 mL water at about 37°C to about 50°C. The prepared sponge was then soaked with water for about 10 minutes to about 30 minutes. After absorbing the water, the sponge was compressed to remove the excess water. 1.9 mL of 12% gelatin (at about 37° to about 50°C) was then added to the sponge, spread and blended with the sponge using a spatula. After 10 minutes, the mixture became a putty like material. This putty material is cohesive and malleable, held its shape and did not wash away (disintegrate) after soaking in water. SEM imaging (Figure 13) showed that this putty material has fibrillar collagen and a three-dimensional porous structure.
The putty may be employed in any clinical or surgical applications where bone void filler, demineralized bone matrix and bone growth factors have been employed, particularly to repair or reconstruct muscular skeleton in a non-weight bearing site. For example, the product can be extruded from a syringe directly onto a defect site or molded into different contour or shape to fit into a surgical site.

Example 4

Exemplary Putty Composition Preparation

In this example, heat denatured collagen is combined with fibrillar collagen, a source of calcium and phosphate and DMB particles to form a putty. A DMB sponge was prepared by whipping 0.125 gram of collagen, 5.4 mL 30 mM hydrochloric acid, 0.156 gram calcium phosphate dibasic (Dical), and 1.25 gram demineralized bone particle into a slurry, followed by lyophilization of the slurry into a 1.2 cm by 0.3 cm by 15 cm sponge. 12% w/v collagen in 0.9% w/v saline or water was heated to 121 °C for 1 to 2 hours to denature the collagen and bring the collagen into solution. 1.2 cm x 0.3 cm x 4 cm portion of the sponge described above was then soaked with water for 10 minutes. After absorbing the water, the sponge was hand compressed to remove the excess water, and then 0.8 mL of the 12% heat denatured collagen solution (at about 37° to about 50°C) was added to the sponge, and spread and blended with the sponge by using a spatula. After 10 minutes, the mixture became a putty like material that was cohesive and malleable, held its shape and did not wash away (disintegrate) after soaking in water.
The putty may be employed in any clinical or surgical applications where bone void filler, demineralized bone matrix and bone growth factors have been employed, particularly to repair or reconstruct muscular skeleton in a non-weight bearing site. For example, the product can be extruded from a syringe directly onto a defect site or molded into different contour or shape to fit into a surgical site.

Example 5

Exemplary Putty Composition Preparation

In this example, a gelatin carrier was included in a fibrillar collagen DMB sponge. The sponge was prepared by whipping 0.125 gram of collagen, 0.005 gram of gelatin, 5.4 mL 20 mM hydrochloric acid, 0.156 gram calcium phosphate dibasic (Dical), and 1.25 gram DMB particles into a slurry, followed by lyophilization of the slurry into a 1.2 cm by 15 cm sponge. After rehydration of the sponge with water (neutral pH, e.g., pH 7.0), the sponge became flexible and formed into a putty like material. This putty could be molded into different shapes and held its shape in water.
The putty may be employed in any clinical or surgical applications where bone void filler, demineralized bone matrix and bone growth factors have been employed, particularly to repair or reconstruct muscular skeleton in a non-weight bearing site. For example, the product can be extruded from a syringe directly onto a defect site or molded into different contour or shape to fit into a surgical site.

Example 6

Exemplary Implant Shapes

In one embodiment, a sponge may be employed for spine defects or injuries, e.g., in a bar with dimensions at about 1 mm (W) x about 2 mm (L) x about 4 to about 5 mm (T), about 10 mm (W) x about 50 mm (L) x about 4 mm to about 5 mm (T) or about 2 mm (W) x about 100 mm (L) x about 4 mm to about 5 mm (T). Other dimensions for a bar include about 10 mm (W) x about 20 mm (L) x about 5 mm (T), about 20 mm (W) x about 50 mm (L) x about 5mm (T), or about 20 mm (W) x about 100 mm (L) x about 5 mm(T). In one embodiment, the sponge may be employed as a strip for a defect such as in scoliosis, with dimensions of about 12 mm (W) x about 10 mm (L) x about 8 mm to about 10 mm (T), and a lip of about 15 mm (1) x about 5 mm to about 6 mm (h), or about 12 mm (W) x about 20 mm (L) x about 8 mm to about 10 mm (T), with a lip of about 15 mm (1) x about 5 mm to about 6 mm (h) (Figure 14A). Other dimensions for a strip include about 12 mm (W) x about 100 mm (L) x about 10 mm (T), and a lip of about 15 mm (1) x about 5 mm to about 6 mm (h), or about 12 mm (W) x about 200 mm (L) x about 10 mm (T), with a lip of about 15 mm x about 5 mm to about 6 mm (h). In one embodiment, the sponge may be employed as a vessel, with dimensions of about 25 mm (W) x about 50 mm (L) x about 10 mm (T), where the concavity in the vessel is about 40 mm (1) x about 15 mm (w) x about 5 mm to about 7 mm (h) or with two concavities where the vessel has dimensions of about 25 mm (W) x about 100 mm (L) x about 10 mm (T), and each concavity has dimensions of about 40 mm (1) x about 15 mm (w) x about 5 mm to about 7 mm (h) (Figure 14B). Other dimensions for a vessel include about 25 mm (W) x about 50 mm (L) x about 10 mm (T), with a concavity of about 15 mm (w) x about 20 mm (1) x about 5mm (h), or about 25 mm (W) x about 100 mm (L) x about 10 mm (T), with a concavity of about 15 mm (w) x about 40 mm (1) x about 5 mm (h). Exemplary dimensions for a bullet shape include about 5.5 mm (dia) x about 15 mm (h), about 7 mm (dia) x about 20 mm (h), or about 9 mm (dia) x about 23 mm (h). Exemplary dimensions for a lower ridge include about 6 mm (w) x about 32 mm (1) x about 12 mm (h) and R about 3 mm, and for an upper ridge include about 10 mm (w) x about 30 mm (h) x about 10 mm (h), and R about 0.8 mm, about 1.8 mm, or about 2.8 mm. The sizes of other shapes, e.g., those for introduction into acetabular or intermedullary regions, can be determined by one of skill in the art.

In one embodiment, the sponge may be employed in dental applications. Exemplary shapes and dimensions for dental implants are provided in Tables 2-6 (see also Figure 15).

Table 2

	Dimensions
Shape of sponge	Diameter (mm)	x	Height (mm)
Capsule	7	x	25
Capsule	11	x	30
Capsule	15	x	30

Table 3

	Dimensions of sponge
Shape of sponge	Diameter (mm)	x	Height (mm)
Bullet	7	x	25
Bullet	9	x	25

Table 4

	Dimensions
Shape of sponge	Length (mm)	x	Width (mm)	x	Height (mm)
Sheet	15	x	20	x	3-4
Sheet	20	x	30	x	3-4

Table 5

	Dimensions
Type of sponge	Length (mm)	x	Diameter (mm)	x	Height (mm)
Upper ridge	30	x	10	x	10
Lower ridge	32	x	6	x	12

Table 6

	Small	Medium	Large
Upper ridge	Height of concave curve: 0.8 mm	Height of concave curve: 1.8 mm	Height of concave curve: 2.8 mm
Lower ridge	Height of concave curve: 0.4 mm	Height of concave curve: 1.7 mm	Height of concave curve: 2.4 mm

Example 7

Bone forming activity of implant with calcium acetate as a mineral component

Various test samples (Table 7), as described below, were implanted subcutaneously in athymic rats to evaluate the compositions with respect to their efficacy for bone growth. Male athymic rats, about seven weeks old at the commencement of the study, were used. Surgery on each rat was performed as follows. Prior to the surgery, the rats were anesthetized by intraperitoneal injection of ketamine/Xylazine solution; 70 mg/kg of ketamine and 5 mg/kg of xylazine. General anesthesia was noted by a lack of response to a toe pinch. Anesthesia was maintained with isoflurane, if needed.
The ventral and dorsal thoracic area of each rat was swabbed with chlorhexadine and alcohol scrub. Using a scalpel or scissors, a 1 cm incision was made in the skin on the right side. This ventral incision was made at the base of the rib cage. After incision, a pocket was prepared beneath the skin and above the incision by blunt dissection towards the axilla. A large blood vessel (cranial thoracodorsal vein) was noted which was often adhered to the skin/subcutaneous tissues. The right ventral implant was placed in the pocket of the subcutaneous tissue approximately 5 mm anterior to the incisions on the chest wall directly below the cranial thoracodorsal blood vessel. When the right ventral side was implanted, the left side had the same procedure done for implantation. The rat was then repositioned to make two more small (1 cm) incisions in the skin of the dorsal thorax. The two dorsal implants were placed toward the middle of the rib cage. All wound closure was accomplished using either stainless steel wound clips or sutures. Thus, each rat had four subcutaneous implants with bilateral placements of the test articles in each of the ventral and dorsal thoracic regions. Figure 3 is a representative image of a rat ventral and dorsal views depicting subcutaneous implant sites Q1-Q4.

Three different types of systems were evaluated: implants containing collagen and DMB, implants containing collagen, DMB, and BMP-2, and implants containing collagen, DMB, and varying amounts and combinations of salts (i.e., calcium acetate, DiCal, trisodium phosphate, or hydroxyapatite). Nominal total salt concentrations evaluated were 10 and 19 weight percent relative to the combined weight of total salt components and the total weight of collagen, accounting for collagen contained in the carrier as well as any collagen found in other components, including the demineralized bone, which was assumed for purposes of experimentation to be 90% by weight collagen. DMB particles were provided by AlloSource, Inc..

Table 7

Group No	Implant Material
A	Collagen + DMB
B	Collagen + DMB + BMP-2 (1.0 µg)
C	Collagen + DMB + CaAc 10%
D	Collagen + DMB + CaAc 19%
E	Collagen + DMB + Na₃PO₄ + CaAc 10%
F	Collagen + DMB + DiCal + CaAc 10%
G	Collagen + DMB + DiCal + CaAc 19%
H	Collagen + DMB + HA 19%
I	Collagen + DMB + DiCal 10%
J	Collagen + DMB + DiCal 19%

Implants with different compositions (Table 8) were generally prepared as follows. Hydrochloric acid (30 mM) was added to the collagen to wet the collagen. The combination was then whipped with a lab scale mixer to obtain a composition with a gel-like consistency. The appropriate amount of DMB powder was added and mixed thoroughly with a spatula to obtain a putty-like consistency. Discs of a desired shape residing on a glass plate were filled with the putty. A second glass plate was positioned over the discs and clamped into place. The glass plate assembly was frozen, generally for a minimum of one hour at -80 °C. The discs were removed from the freezer and excess material was trimmed from the disc molds. The glass plate assembly was quickly returned to the freezer again for a minimum of one hour at -80 °C. The assembly was then subjected to lyophilization for a minimum of 12 hours. The resulting sponge implants were then recovered from the molds.

Table 8

Groups	Carrier (g)	DMB (g)	Mineral (g)	HCl (mL)	BMP-2 (µg)
Collagen + DMB	0.125	1.25	N/A	5.4	N/A
Collagen + DMB + BMP-2	0.125	1.25	N/A	5.4	1
Collagen + DMB + CaAc 10%	0.125	1.25	CaAc 0.156 g	5.4	N/A
Collagen + DMB + CaAc 19%	0.125	1.25	CaAc 0.3125 g	5.4	N/A
Collagen + DMB + Na₃PO₄ + CaAc 10%	0.125	1.25	Na₃PO₄ 0.096 g; CaAc 0.06 g	5.4	N/A
Collagen + DMB + DiCal + CaAc 10%	0.125	1.25	CaAc 0.068 g; Dical: 0.088 g	5.4	N/A
Collagen + DMB + DiCal + CaAc 19%	0.125	1.25	CaAc 0.136 g; Dical: 0.176 g	5.4	N/A
Collagen + DMB + HA 19%	0.125	1.25	HA 0.3125 g	5.4	N/A
Collagen + DMB + DiCal 10%	0.125	1.25	Dical 0.156 g	5.4	N/A
Collagen + DMB + DiCal 19%	0.125	1.25	Dical 0.3125 g	5.4	N/A

For implants intended to contain various amount of salts or combinations of different salts, the appropriate amount of salt was added to the combination of hydrochloric acid and collagen prior to the whipping step. The combination of collagen, hydrochloric acid, and DiCal was first mixed with a spatula and then whipped with a mixer.
For implants intended to contain BMP-2, 20 µL of reconstituted BMP-2 (0.25 µg/µL in 4 mM HCl) was added to one side of the lyophilized sponge implant disc followed by adding another 20 µL of the reconstituted BMP-2 to the other side of the lyophilized sponge implant discs. The BMP-2 solution was allowed to soak into the sponge implant disc. The sponge implant disc was subjected to freezing conditions for one hour at -80 °C. The assembly was then subjected to lyophilization for a minimum of 12 hours. The resulting sponge implants were then recovered.
After 28 days, the implants were removed for radiographic evaluation. The explants were fixed in 10% NBF and radiographed. The representative radiographs from each treatment group are depicted in Figure 16. The radiograph showed that the presence of DiCal, calcium acetate, or calcium acetate combined with Dical or trisodium phosphate enhanced bone formation at the concentrations evaluated.

Example 8

Fusion activity following defect filling

A critical size defect (5 mm) in the left femur of a rat was filled with one of four compositions (see Table 9) in the form of a cylinder about 6 mm in length and about 3 mm in diameter; 1) a bone void filler composition of the invention; 2) a composition formed with collagen and BMP-2; 3) a composition formed with collagen and DBM; or 4) Puros^® DBM. Radiographs of the filled defect were taken at 4 to 8 weeks post-filling, and micro CT scans were taken at 8 weeks post-filling.

The radiographs taken at 4 weeks are shown in Figure 17. Collagen plus DMB and Puros^® DBM did not induce fusion at any of 8 defects while a bone void filler composition of the invention and a composition formed with collagen and BMP-2 resulted in fusion of 6/8 defects. Collagen and BMP-2 may have shown better fusion than a bone void filler composition of the invention at 8 weeks.

Table 9

Group	Carrier (g)	DBM (g)	Mineral (g)	HCl (mL)	BMP-2 (µg)
Collagen + DBM + Mineral	0.223	2.013	0.265	9.2	N/A
Collagen + BMP-2	1.000	N/A	N/A	41.2	10
Collagen + DBM	0.250	2.250	N/A	10.3	N/A
Puros® DBM Putty	N/A	N/A	N/A	N/A	N/A
Empty defect	N/A	N/A	N/A	N/A	N/A

Example 9

Biocompatible fibers for use in a bone void filler composition

To create or increase load bearing capabilities, and thus the structural integrity, in a material that is introduced around or into a void or fracture, which material is absorbed over time and is replaced by good quality bone, a biocompatible and biodegradable fiber is added to a bone void filler composition of the invention. The weight percentage of the fibers can vary based upon the desired properties, e.g., strength, biologic properties, handling characteristics. In one embodiment, the weight percentage of fiber may be from about 10 % to about 70%. Typically, as the fiber length decreases, the percentage of fill decreases in order to achieve the desired strength.
For example, bioactive glass (a.k.a. Bioglass) fibers are incorporated into a bone void filler composition. The bioactive glass fibers act as fiber reinforcement and increase the mechanical properties of the material and/or provide for more robust handling properties. One example of a biocompatible fiber is 45S5, which is composed of calcium salts, phosphorous, sodium salts and silicates (45S5 is 46.1 SiO₂, 26.9 CaO, 24.4 Na₂O and 2.5 P₂O₅ (mol%)) which are essential elements of mineralized bone. Other bioglass compositions include, but are not limited to, 58S which is 60 SiO₂, 36 CaO and 4 P₂O₅ (mol%), S70C30 which is 70 SiO₂ and 30 CaO (mol%), and 13-93 which is 6.0 Na₂O 7.9 K₂O, 7.7 MgO, 22.1 CaO, 1.7 P₂O₅, 54.6 SiO₂ (mol.%). Yet other biocompatible fibers include SSSE which is 54.1 SiO₂, 22.3 CaO, 19.8 Na₂O, 1.3 P₂O₅ and 8.7 CaF (mol%) and SS3P4 which is 54.2 SiO₂, 22 CaO, 22.9Na₂O and 0.9 P₂O₅ (mol%)
Various compositions that incorporate bioactive glass have been shown to bond with bone and promote bone regeneration while it is resorbed by the body. The breakdown of the bioactive glass proivdes essential mineral elements to an area but does not create an undesirable localized pH which would retard the bone formation/healing process. In another embodiment, the bioactive glass may be fabricated as a mat, e.g., one that is cut to a desired shape, then a bone void filler composition is added to the mat, e.g., pressed into it.

Example 10

Bone forming activity of demineralized bone putty implants

Various test samples (Table 10), as described below, were implanted subcutaneously in athymic rats to evaluate the compositions with respect to their efficacy for bone growth. Male athymic rats, about seven weeks old at the commencement of the study, were used. Surgery on each rat was performed as follows. Prior to the surgery, the rats were anesthetized by intraperitoneal injection of ketamine/Xylazine solution; 70 mg/kg of ketamine and 5 mg/kg of xylazine. General anesthesia was noted by a lack of response to a toe pinch. Anesthesia was maintained with isoflurane, if needed.
The ventral and dorsal thoracic area of each rat was swabbed with chlorhexadine and alcohol scrub. Using a scalpel or scissors, a 1 cm incision was made in the skin on the right side. This ventral incision was made at the base of the rib cage. After incision, a pocket was prepared beneath the skin and above the incision by blunt dissection towards the axilla. A large blood vessel (cranial thoracodorsal vein) was noted which was often adhered to the skin/subcutaneous tissues. The right ventral implant was placed in the pocket of the subcutaneous tissue approximately 5 mm anterior to the incisions on the chest wall directly below the cranial thoracodorsal blood vessel. When the right ventral side was implanted, the left side had the same procedure done for implantation. The rat was then repositioned to make two more small (1 cm) incisions in the skin of the dorsal thorax. The two dorsal implants were placed toward the middle of the rib cage. All wound closure was accomplished using either stainless steel wound clips or sutures. Thus, each rat had four subcutaneous implants with bilateral placements of the test articles in each of the ventral and dorsal thoracic regions. Figure 3 is a representative image of a rat ventral and dorsal views depicting subcutaneous implant sites Q1-Q4.
Three different types of systems were evaluated: 1) implants containing fibrillar collagen and DMB; 2) implants containing fibrillar collagen and BMP-2; 3) implants containing fibrillar collagen, gelatinized collagen, DMB, with or without calcium hydrogen phosphate (DiCal) (see Table 10). DMB particles were provided by AlloSource, Inc..
Implants were prepared as follows. To prepare sponge implants, the procedure is as follows. Hydrochloric acid (30 mM) was added to the collagen to wet the collagen. The combination was then whipped with a lab scale mixer to obtain a composition with a gel-like consistency. The appropriate amount of DMB powder was added and mixed thoroughly with a spatula to obtain a putty-like consistency. Discs of a desired shape residing on a glass plate were filled with the putty. A second glass plate was positioned over the discs and clamped into place. The glass plate assembly was frozen, generally for a minimum of one hour at -80 °C. The discs were removed from the freezer and excess material was trimmed from the disc molds. The glass plate assembly was quickly returned to the freezer again for a minimum of one hour at -80 °C. The assembly was then subjected to lyophilization for a minimum of 12 hours. The resulting sponge implants were then recovered from the molds. To prepare putty implants, the procedure is as follows. The prepared DMB containing sponges (as previously described) were hydrated with 20 mL deionized water and hydrated for 10 min. After hydration, the excess water was removed by squeezing the water out. Then 0.6 mL gelatinized collagen (per gram of dry weight sponge material), which were prepared by heating 12% collagen in saline solution at 121°C for 1 hr, was added to the hydrated sponge and thoroughly mixed with the hydrated sponge. After 1-2 min mixing, the materials became a putty. About 0.1 gram of this material was weighed and implanted into rats.
For implants intended to contain various amount of salts or combinations of different salts, the appropriate amount of salt was added to the combination of hydrochloric acid and collagen prior to the whipping step. The combination of collagen, hydrochloric acid, and DiCal was first mixed with a spatula and then whipped with a mixer.
For implants intended to contain BMP-2, 20 µL of reconstituted BMP-2 (0.25 µg/µL) was added to one side of the lyophilized sponge implant disc followed by adding another 20 µL of the reconstituted BMP-2 to the other side of the lyophilized sponge implant discs. The BMP-2 solution was allowed to soak into the sponge implant disc. The sponge implant disc was subjected to freezing conditions for one hour at -80 °C. The assembly was then subjected to lyophilization for a minimum of 12 hours. The resulting sponge implants were then recovered.

After 28 days, the implants were removed for radiographic evaluation. The explants were fixed in 10% NBF and radiographed. The radiographs from each treatment group are depicted in Figure 18. The radiograph showed DBM putty with DiCal (formulated with fibrillar collagen and gelatinized collagen) enhanced bone formation compared to DBM putty without DiCal and DMB particles with collagen only.

Table 10

Groups	Fibrillar Collagen (a)	DMB (g)	Mineral (g)	HCl (mL)	BMP-2 (µg)	Gelatinized collagen (g)	0.9% saline (mL)
Fibrillar Collagen + DMB (sponge)	0.125	1.25	N/A	5.4	N/A	N/A	N/A
Fibrillar Collagen +BMP-2 (sponge)	0.125	1.25	N/A	5.4	1	N/A	N/A
Fibrillar Collagen + DMB + heat gelatinized collagen (putty)	0.125	1.25	Dical 0.156 g	5.4	N/A	0.101	0.8
Fibrillar Collagen + DMB +heat gelatinized collagen +Dical 19%) (putty)	0.125	1.25	Dical 0.156 g	5.4	N/A	0.134	1.2

Example 11

Effect of varying amounts of calcium phosphate on posterio-lateral spine fusion

Materials and Methods

Treatment Groups. Animals (males) were randomized into treatment groups, based on body weights collected following arrival (Table 11). The mean bodyweights for each group were reviewed to ensure that the group mean and standard deviation values satisfy the assumption of homogeneity. Group allocations were documented in the study records. Each animal received an implant from the same group on both the left side and the right side.

Table 11.

Group	Surgery	Treatment	Dose	# Animals
Group	Surgery	Treatment	Dose
1	Bilateral lumbar implant	DBM	n.a.	4
2	Bilateral lumbar implant	DBM	1 + BMP-2	2 µg/rat	3
3	Bilateral lumbar implant	DBM	1 + Calcium phosphate mineral 0.5%	n.a.	4
4**	Bilateral lumbar implant	DBM 2 (Puros® DBM Putty)	0.5 g/side	4
5	Bilateral lumbar implant	DBM	1 + Calcium phosphate mineral 2.5%	n.a.	4
6	Bilateral lumbar implant	DBM	1 + Calcium phosphate mineral 5.0%	n.a.	4
7	Bilateral lumbar implant	Collagen + BMP-2	5 µg/rat	3
8	Negative control	Decortication only on left side	n.a.	2

** Animals from Group 4 were euthanized 4 weeks after surgery. Additionally, Animal 153 (Group 3) was found to be moribund and also euthanized at 4 weeks. All other animals were euthanized 8 weeks after surgery. These animals received oxytetracycline and calcein labels.

Surgery. Anesthesia was induced and maintained according to routine methods. General anesthesia was noted by a lack of response to a toe pinch. Anesthesia was maintained with isoflurane, as necessary. After induction of anesthesia, the rat was placed in ventral recumbency with front and hind legs extended. Using standard laboratory techniques, the spinal region area was clipped or shaved, cleaned and scrubbed as per proper aseptic surgical technique.
L4-L5 posteriolateral fusions were performed, as follows. The spine was approached through a single midline skin incision and two separate muscle incisions, one to the left and one to the right side of the vertebral column, were made to approach the spine. The level was identified during surgery by referencing from the pelvis. Once exposed, the transverse processes of L4 and L5 on both sides were decorticated. Implant material was then placed in the posteriolateral gutters as described.
The fascia was closed with sutures. The skin was closed with sutures or staples. Any staples or sutures remaining 14 days post-op were removed under isoflurane anesthesia.
Implant Material Placement. Back muscles attached to the transverse processes are lifted and the implant was placed below the muscle spanning L4 and L5 transverse processes, to secure the implant in place.
Oxytetracycline and Calcein Labels. One dose of oxytetracycline (30 mg/kg body weight; Sigma 05875) was given to each animal 6 days prior to sacrifice and one dose of calcein (10 mg/kg) was given to each animal 2 days prior to sacrifice.
Mechanical Stability Testing. Mechanical stability was assessed on all samples immediately following tissue collection by manual palpation. Two individuals blinded to the group assignment for treatment assessed the stability of each animal using the scoring system below, as described by Qui et al. (J. Biomed. Mat. Res., 82B:239 (2007)):

Manual palpation score

0: - empty
1: - some bumps
2: - some gaps
3: - small gaps
4: - completely bridged

Histology. Spine segments harvested from the study were processed for undecalcified bone histology. Two sections from each block were prepared; one from the transverse or cross-sectional plane and the other from the sagittal plane along the spine column that include the fusion mass on each side of the spinal column. The sections were stained with Masson's trichrome (see Figures 19, 21 and 23). Additionally, one slide from each plane was left unstained for fluorochrome microscopy (see Figures 22-23).

Table 12. Scoring criteria

Parameter	Score	Definition
Fibrosis	-1 to -4	Amount of fibrotic tissue present in the marrow and/or surrounding the implanted pieces (-4 is extensive fibrosis).
Inflammation	-1 to -4	Severity of inflammatory cells accumulation and infiltration in and around the implanted area (-4 is extensive inflammation).
New bone segments	1 to 4	Indicates the presence of a bony area that does not come from the Periosteal bony proliferation of the implant or existing bone
New bone on implant surfaces	1 to 4	Indicates the presence of new lamellar bone added to the cancellous bone surfaces within the implant pieces
New cartilage	1 to 4	Indicates the presence of new cartilage in and around the implant pieces, besides the remnant growth plates in some of the implant pieces
Fusion of implants and existing bone	1 to 4	Indicates the extent of surface contact by the callus formed between the implant pieces and existing bone
Fusion of implants	1 to 4	Indicates the extent of surface contact by the callus formed between the implant pieces
Amount of new bone	1 to 4	Indicated the extent of surface showing fluorochrome labels in the
labeled		fusion area

Results

A total of 26 male athymic rats (Hsd:RH-Foxnl^rnu ), 3 months old upon arrival, except those in the negative control group (2 animals), had bilateral surgeries implanted with a test article in the right and left posterior-lateral gutters between L4 and L5. The negative control group did not receive any implant on the decorticated side.
Following implantation, rats were observed for clinical signs of complications for 3 days. Body weights were determined at the start of the study and weekly thereafter. Four weeks post-surgery, 2 males from Group 4 Puros^® DBM Putty were sacrificed and the lumbar segment containing the fusion masses removed. Eight weeks post-surgery, all rats, with the exception of animals from Group 4, were sacrificed and the lumbar segment containing the fusion masses removed. Before each sacrifice, all animals were given one dose of oxytetracycline (30 mg/kg body weight) 6 days prior to sacrifice and one dose of calcein 2 days prior to sacrifice.
Mechanical stability was assessed by manual palpation on all samples. The spine samples (T13-S1 region) were placed in 10% neutral buffered formalin and radiographed. The radiographs were scored. Complete fusion was deemed present if bridging bone was noted completely in inter-transverse region. Preserved samples were subjected to micro-CT analysis.
The radiographic results indicated good spinal fusion with DBM 1, DBM 1 + 2.5% or 5% calcium phosphate mix, DBM 1 + BMP-2, and collagen + BMP-2, however, the density of the fusion mass in collagen + BMP-2 was significantly less than that of DBM 1. DBM 1 + 0.5% calcium phosphate mineral mix and DBM 2 (Puros® DBM Putty) showed significantly less complete fusion and density when compared to DBM 1. There was no fusion mass noted in any animal in the negative control group.

Results for mechanical stability of the fusion area were compared to DBM 1 treated group (Group 1). There were significant reductions of mechanical stability score in animals treated with DBM 1 + 0.5% calcium phosphate mineral and collagen + BMP-2, when compared to DBM 1-treated animals (Table 13). There was a positive trend of enhanced mechanical stability with increasing calcium phosphate mineral amounts.

Table 13. Mechanical Stability

Treatment Group	Data	Tester A	Tester B

Group
1	Mean	4.00	4.00
DBM 1	SD	0.00	0.00
	Stat	# n.a.	n.a.
Group 2	Mean	4.00	4.00
DBM 1 + BMP-2	SD	0.00	0.00
	Stat	n.s.^&	n.s.
Group 3	Mean	1.25	1.50
DBM 1 + Calcium phosphate mineral 1.0%	SD	0.96	1.29
DBM 1 + Calcium phosphate mineral 1.0%	Stat	0.0020	0.2110
Group 4	Mean	2.00	2.00
DBM 2	SD	2.31	2.31
(Puros® DBM Putty)	Stat	n.s.	n.s.
Group 5	Mean	3.00	3.50
DBM 1 + Calcium phosphate mineral 5%	SD	0.82	0.58
DBM 1 + Calcium phosphate mineral 5%	Stat	n.s.	n.s.
Group 6	Mean	3.75	3.75
DBM 1 + Calcium phosphate mineral 10.0%	SD	0.50	0.50
DBM 1 + Calcium phosphate mineral 10.0%	Stat	n.s.	n.s.
Group 7	Mean	1.67	1.67
Collagen + BMP-2	SD	0.58	0.58
	stat	0.0301	0.0301
Group 8	Mean	1.50	1.50
Decortication only on left side	SD	2.12	2.12
Decortication only on left side
Negative control	Stat	n.s.	n.s.

• Stat = a non-parametric rank sum Wilcoxon test
• # n.a. = not applicable
& n.s. = not significant when compared to Group 1 control group

The data from the histology scores showed remarkable differences between DBM 1 and Puros® DBM putty; the former facilitated a better overall outcome for osteoinductivity or bone formation in this spinal fusion model. From the total scores, good overall fusion was evident with DBM 1 or the DBM 1 combined with BMP-2 or 10% CaP indicating that this combination may reduce the bulk amount of DBM 1 needed to fill in the space between the spinal processes of the two adjacent vertebral segments. Overall, there was more fusion mass evident with DBM 1 + 10% CaP compared to that with collagen + BMP-2. The proportion of added CaP may indicate the advantage to have a higher percentage in fusing the vertebral segments.

The score for each parameter was summed for all animals in a group and the averages of the scores in the sagittal and transverse planes are shown in Tables 14 and 15, respectively. Groups 4 (Puros® DBM Putty), 7 (Collagen + BMP-2) and 8 (Decortication only) showed the least fusion activities, while Groups 1 (DBM 1), 2 (DMB 1 + BMP-2), and 6 (DBM 1 + 10% CaP) had significantly more fusion tissues formed. There was a positive trend in fusion and bone formation with increasing calcium phosphate amounts. For many of the measures of bone growth and fusion, the addition of calcium phosphate mineral provided similar or better results than the addition of exogenous BMP-2, particularly at the highest calcium phosphate mineral amount tested. Moreover, the highest calcium phosphate mineral amount employed in implants did not induce fibrosis or inflammation to any greater extent in the sagittal plane relative to implants with exogenous BMP-2. Although the fibrosis and inflammation scores for the highest calcium phosphate amount were greater in the transverse plane relative to BMP-2 implants, the amount of fibrosis and inflammation that was observed was within the acceptable range for implants.

Table 14. Summary of Histology Results - Sagittal Plane (Longitudinal)

Parameter	Data	G1	G2	G3	G4	G5	G6	G7	G8
Fibrosis	Mean	0.67	0.5	1.5	2	2	0.33	0	0
	StDev	0.58	0.71	2.12	0	1	0.58	0	N/A
	Count	3	2	2	2	3	3	3	1
Inflammation	Mean	1	0.5	0.5	1.5	1	0.33	0	0
	StDev	0	0.71	0.71	0.71	0	0.58	0	N/A
	Count	3	2	2	2	3	3	3	1
New bone segments	Mean	0	0	0	0	0.67	0	0	0
	StDev	0	0	0	0	1.15	0	0	N/A
	Count	3	2	2	2	3	3	3	1
New bone on implant	Mean	1	2	1	0.5	2	2	0	0
New bone on implant	StDev	0	0	0	0.71	1	1	0	N/A

surfaces	Count	3	2	2	2	3	3	3	1
New cartilage	Mean	0.33	0	0	0	0.67	0	0	0
	StDev	0.58	0	0	0	1.15	0	0	N/A
	Count	3	2	2	2	3	3	3	1
Fusion of implants and existing bone	Mean	4	3	2.5	0	3.67	4	0	0
	StDev	0	1.41	0.71	0	0.58	0	0	N/A
	Count	3	2	2	2	3	3	3	1
Fusion of implants	Mean	3.67	3.5	1.5	0.5	3.33	4	0	0
	StDev	0.58	0.71	0.71	0.71	1.15	0	0	N/A
	Count	3	2	2	2	3	3	3	1
Amount of new bone labeled	Mean	2.33	2	2.5	0.5	2.67	2.67	0	0
	StDev	1.53	0	0.71	0.71	0.58	1.53	0	N/A
	Count	3	2	2	2	3	3	3	1

Table 15- Summary of Histology Results - Transverse Plane (Cross-Sectional)

Parameter	Data	G1	G2	G3	G4	G5	G6	G7	G8
Fibrosis	Mean	0.33	0.50	2.00	2.50	2.33	1.33	0.00	0.00
	StDev	0.58	0.71	0.00	0.71	0.58	0.58	0.00	N/A
	Count	3	2	2	2	3	3	3	1
Inflammation	Mean	0.33	0.50	1.50	1.50	1.00	1.00	0.00	0.00
	StDev	0.58	0.71	0.71	0.71	0.00	0.00	0.00	N/A
	Count	3	2	2	2	3	3	3	1
New bone segments	Mean	0.00	0.00	0.00	0.00	0.00	0.00	0.00	0.00
	StDev	0.00	0.00	0.00	0.00	0.00	0.00	0.00	N/A
	Count	3	2	2	2	3	3	3	1
New bone on implant surfaces	Mean	2.00	1.50	1.00	0.50	1.00	2.00	0.33	0.00
	StDev	1.00	0.71	0.00	0.71	1.00	1.00	0.58	N/A
	Count	3	2	2	2	3	3	3	1
New cartilage	Mean	0.00	0.00	0.00	0.00	0.33	0.00	0.00	0.00
	StDev	0.00	0.00	0.00	0.00	0.58	0.00	0.00	N/A
	Count	3	2	2	2	3	3	3	1
Fusion of implants and existing bone	Mean	3.00	3.00	2.00	0.50	1.00	3.33	1.33	0.00
	StDev	1.00	1.41	1.41	0.71	1.00	0.58	2.31	N/A
	Count	3	2	2	2	3	3	3	1
Fusion of implants	Mean	4.00	4.00	2.50	0.50	1.00	4.00	1.33	0.00
	StDev	0.00	0.00	0.71	0.71	1.73	0.00	2.31	N/A
	Count	3	2	2	2	3	3	3	1
Amount of new bone labeled	Mean	2.00	2.00	2.00	0.50	1.67	2.33	1.00	0.00
	StDev	1.00	0.00	0.00	0.71	1.15	1.53	1.73	N/A
	Count	3	2	2	2	3	3	3	1

In summary, the bone void filler compositions of the invention had a fusion rate similar to compositions with BMP-2. In addition, the fusion mass for animals treated with bone void filler compositions of the invention was significantly larger than for animals treated with compositions with BMP-2. Also, a larger trabecular volume was observed in animals treated with bone void filler compositions of the invention. Treatment with the bone void filler compositions of the invention result in more new bone forming regions, consistent with increased new bone volume.
Therefore, the present invention is well adapted to attain the ends and advantages mentioned as well as those that are inherent therein. The particular embodiments disclosed above are illustrative only, as the present invention may be modified and practiced in different but equivalent manners apparent to those skilled in the art having the benefit of the teachings herein. For example, while the primary intended use of the composition of the present invention is for use as a bone void filler, it is envisioned that the composition could be used for other purposes. It is therefore evident that the particular illustrative embodiments disclosed above may be altered or modified and all such variations are considered within the scope and spirit of the present invention. The indefinite articles "a" or "an", as used in the claims, are defined herein to mean one or more than one of the element that it introduces.
Where a range of values is provided, it is understood that each intervening value, unless the context clearly dictates otherwise, between the upper and lower limit of that range and any other stated or intervening value in that stated range, is encompassed within the invention. The upper and lower limits of these smaller ranges may independently be included in the smaller ranges, and such embodiments are also encompassed within the invention, subject to any specifically excluded limit in the stated range. Where the stated range includes one or both of the limits, ranges excluding either or both of those included limits are also included in the invention.

Claims

A bone void filler composition comprising:
an acidic calcium phosphate component from 8 wt% to 12 wt% of the composition;

an osteoinductive demineralized bone component from 70 wt% to 80 wt% of the composition; and

an osteoconductive collagen carrier component comprising from 10 wt% to 16 wt% of the composition ;
wherein the composition is in the form of a porous three dimensional structure and the composition has a pH from 3 to 5.
The bone void filler composition of claim 1, wherein the acidic calcium phosphate component comprises monocalcium phosphate monohydrate [Ca(H₂PO₄)2H₂O]; calcium hydrogen phosphate dihydrate [CaHPO₄2H₂O], amorphous calcium phosphate [Ca₃(PO₄)2H₂O], anhydrous calcium hydrogen phosphate [CaHPO₄], partially dehydrated calcium hydrogen phosphate [CaHPO₄xH₂O, where x is between 0 and 2], and/or calcium pyrophosphate (Ca₂O₇P₂) [2CaO₂P₂O₅].
The bone void filler composition according to claim 1, wherein the bone void filler composition is in the form of a sponge or in the form of a paste or putty obtained from particulated sponge.
The bone void filler composition according to any preceding claim, wherein the bone void filler composition further comprises a liquid carrier.
The bone void filler composition according to claim 4, wherein the liquid carrier comprises one or more liquid carriers selected from the group consisting of i) biological fluids selected from the group consisting of bone marrow aspirate, whole blood, serum, and plasma, ii) biocompatible liquids selected from the group consisting of water, saline, buffers, or liquids comprising glycerin, glycerol, lecithin, surfactants, carboxylic acids, dimethylsulfoxide, and tetrahydrofuran; iii) natural and synthetic polymers selected from the group consisting of aliphatic polyesters, polyethylene glycols, polyanhydrides, dextran polymers, and polymeric orthophosphates; and combinations thereof.
The bone void filler composition according to any one of claims 1 to 4, wherein the bone void filler composition is injectable.
The bone void filler composition according to claim 2, further comprising an additive selected from the group consisting of allograft chips, bioceramics, biocomposites, calcium salts other than DiCal, phosphate salts other than DiCal; and combinations thereof.
The bone void filler composition according to any one of claims 1 to 7, wherein the demineralized bone has been provided in a form selected from powder, particulate, granule, fiber, and combinations thereof.
The bone void filler composition according to any one of claims 1 to 8, the bone void filler composition further comprising a bone growth factor component.
The bone void filler composition according to any one of claims 1 to 9, wherein the demineralized bone comprises demineralized bone derived from a human.
The bone void filler composition according to claim 1 wherein the collageneous biologically acceptable carrier comprises gelatin or heat denatured and solubilized collagen.